fix: improve Windows browser autodetection paths and diagnose fallback (#816)

## ℹ️ Description
This pull request fixes Windows browser auto-detection failures reported
by users where `diagnose`/startup could not find an installed browser
even when Chrome or Edge were present in standard locations. It also
makes diagnostics resilient when auto-detection fails by avoiding an
assertion-driven abort and continuing with a clear failure log.

- Link to the related issue(s): Issue #815
- Describe the motivation and context for this change.
- Users reported `Installed browser could not be detected` on Windows
despite having a browser installed.
- The previous Windows candidate list used a mix of incomplete paths and
direct `os.environ[...]` lookups that could raise when variables were
missing.
- The updated path candidates and ordering were aligned with common
Windows install locations used by Playwright’s channel/executable
resolution logic (Chrome/Edge under `LOCALAPPDATA`, `PROGRAMFILES`, and
`PROGRAMFILES(X86)`).

## 📋 Changes Summary
- Expanded Windows browser path candidates in `get_compatible_browser()`
to include common Google Chrome and Microsoft Edge install paths, while
keeping Chromium and PATH fallbacks.
- Replaced unsafe direct env-var indexing with safe retrieval
(`os.environ.get(...)`) and added a fallback derivation for
`LOCALAPPDATA` via `USERPROFILE\\AppData\\Local` when needed.
- Kept legacy Chrome path candidates
(`...\\Chrome\\Application\\chrome.exe`) as compatibility fallback.
- Updated diagnostics flow to catch browser auto-detection assertion
failures and continue with `(fail) No compatible browser found` instead
of crashing.
- Added/updated unit tests to verify:
  - Windows detection for LocalAppData Chrome/Edge/Chromium paths.
- Missing Windows env vars no longer cause key lookup failures and still
surface the intended final detection assertion.
- `diagnose_browser_issues()` handles auto-detection assertion failures
without raising and logs the expected failure message.


### ⚙️ Type of Change
Select the type(s) of change(s) included in this pull request:
- [x] 🐞 Bug fix (non-breaking change which fixes an issue)


## ✅ Checklist
Before requesting a review, confirm the following:
- [x] I have reviewed my changes to ensure they meet the project's
standards.
- [x] I have tested my changes and ensured that all tests pass (`pdm run
test`).
- [x] I have formatted the code (`pdm run format`).
- [x] I have verified that linting passes (`pdm run lint`).
- [x] I have updated documentation where necessary.

By submitting this pull request, I confirm that you can use, modify,
copy, and redistribute this contribution, under the terms of your
choice.

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Bug Fixes**
* Hardened Windows browser auto-detection: checks additional common
installation locations for Chrome/Chromium/Edge and treats detection
failures as non-fatal, allowing diagnostics to continue with fallback
behavior and debug logging when no browser is found.

* **Tests**
* Expanded Windows detection tests to cover more path scenarios and
added cases verifying failure-mode diagnostics and logging.

* **Style**
  * Minor formatting tweak in default configuration.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

tests/unit/test_web_scraping_mixin.py

@@ -878,6 +878,10 @@ class TestWebScrapingBrowserConfiguration:
                 edge_path,
                 chrome_path,
                 # Windows paths
+                "C:\\Users\\runneradmin\\AppData\\Local\\Google\\Chrome\\Application\\chrome.exe",
+                "C:\\Program Files\\Google\\Chrome\\Application\\chrome.exe",
+                "C:\\Program Files (x86)\\Google\\Chrome\\Application\\chrome.exe",
+                "C:\\Users\\runneradmin\\AppData\\Local\\Microsoft\\Edge\\Application\\msedge.exe",
                 "C:\\Program Files\\Microsoft\\Edge\\Application\\msedge.exe",
                 "C:\\Program Files (x86)\\Microsoft\\Edge\\Application\\msedge.exe",
                 "C:\\Program Files\\Chromium\\Application\\chrome.exe",
@@ -1085,10 +1089,32 @@ class TestWebScrapingBrowserConfiguration:
 
         # Test Windows with environment variables not set
         monkeypatch.setattr(platform, "system", lambda: "Windows")
-        # Set default values for environment variables
         monkeypatch.setenv("PROGRAMFILES", "C:\\Program Files")
         monkeypatch.setenv("PROGRAMFILES(X86)", "C:\\Program Files (x86)")
         monkeypatch.setenv("LOCALAPPDATA", "C:\\Users\\TestUser\\AppData\\Local")
+
+        local_chrome_path = "C:\\Users\\TestUser\\AppData\\Local\\Google\\Chrome\\Application\\chrome.exe"
+        monkeypatch.setattr(os.path, "isfile", lambda p: p == local_chrome_path)
+        assert scraper.get_compatible_browser() == local_chrome_path
+
+        local_edge_path = "C:\\Users\\TestUser\\AppData\\Local\\Microsoft\\Edge\\Application\\msedge.exe"
+        monkeypatch.setattr(os.path, "isfile", lambda p: p == local_edge_path)
+        assert scraper.get_compatible_browser() == local_edge_path
+
+        local_chromium_path = "C:\\Users\\TestUser\\AppData\\Local\\Chromium\\Application\\chrome.exe"
+        monkeypatch.setattr(os.path, "isfile", lambda p: p == local_chromium_path)
+        assert scraper.get_compatible_browser() == local_chromium_path
+
+        monkeypatch.delenv("LOCALAPPDATA", raising = False)
+        monkeypatch.setenv("USERPROFILE", "C:\\Users\\FallbackUser")
+        fallback_local_chrome_path = "C:\\Users\\FallbackUser\\AppData\\Local\\Google\\Chrome\\Application\\chrome.exe"
+        monkeypatch.setattr(os.path, "isfile", lambda p: p == fallback_local_chrome_path)
+        assert scraper.get_compatible_browser() == fallback_local_chrome_path
+
+        monkeypatch.delenv("PROGRAMFILES", raising = False)
+        monkeypatch.delenv("PROGRAMFILES(X86)", raising = False)
+        monkeypatch.delenv("LOCALAPPDATA", raising = False)
+        monkeypatch.delenv("USERPROFILE", raising = False)
         monkeypatch.setattr(os.path, "isfile", lambda p: False)
         with pytest.raises(AssertionError, match = "Installed browser could not be detected"):
             scraper.get_compatible_browser()
@@ -1350,7 +1376,7 @@ class TestWebScrapingDiagnostics:
 
     def test_diagnose_browser_issues_auto_detect_failure(self, scraper_with_config:WebScrapingMixin, caplog:pytest.LogCaptureFixture) -> None:
         """Test diagnostic when auto-detecting browser fails."""
-        with patch.object(scraper_with_config, "get_compatible_browser", return_value = None):
+        with patch.object(scraper_with_config, "get_compatible_browser", side_effect = AssertionError("No browser found")):
             scraper_with_config.browser_config.binary_location = None
             scraper_with_config.diagnose_browser_issues()
 
@@ -1748,9 +1774,9 @@ class TestWebScrapingDiagnostics:
         with patch("platform.system", return_value = "Linux"), \
                 patch("kleinanzeigen_bot.utils.web_scraping_mixin._is_admin", return_value = False), \
                 patch("psutil.process_iter", return_value = []), \
-                patch.object(scraper_with_config, "get_compatible_browser", side_effect = AssertionError("No browser found")), \
-                pytest.raises(AssertionError, match = "No browser found"):
+                patch.object(scraper_with_config, "get_compatible_browser", side_effect = AssertionError("No browser found")):
             scraper_with_config.diagnose_browser_issues()
+            assert "(fail) No compatible browser found" in caplog.text
 
     def test_diagnose_browser_issues_user_data_dir_permissions_issue(
             self, scraper_with_config:WebScrapingMixin, caplog:pytest.LogCaptureFixture, tmp_path:Path