fix: publishing contact fields and download stability (#771)

## ℹ️ Description
- Link to the related issue(s): Issue #761
- Describe the motivation and context for this change.
- This PR bundles several small fixes identified during recent testing,
covering issue #761 and related publishing/download edge cases.

## 📋 Changes Summary
- Avoid crashes in `download --ads=new` when existing local ads lack an
ID; skip those files for the “already downloaded” set and log a clear
reason.
- Harden publishing contact fields: clear ZIP before typing; tolerate
missing phone field; handle missing street/name/ZIP/location gracefully
with warnings instead of aborting.
- Improve location selection by matching full option text or the
district suffix after ` - `.
- Preserve `contact.location` in defaults (config model + regenerated
schema with example).

### ⚙️ 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)
- [ ] ✨ New feature (adds new functionality without breaking existing
usage)
- [ ] 💥 Breaking change (changes that might break existing user setups,
scripts, or configurations)

## ✅ 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

## Release Notes

* **New Features**
* Added optional location field to contact configuration for specifying
city/locality details in listings.
* Enhanced contact field validation with improved error handling and
fallback mechanisms.

* **Bug Fixes**
* Ad download process now gracefully handles unpublished or manually
created ads instead of failing.

* **Documentation**
* Clarified shipping type requirements and cost configuration guidance
in README.

<sub>✏️ Tip: You can customize this high-level summary in your review
settings.</sub>

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

README.md

@@ -276,7 +276,7 @@ ad_defaults:
   price_type: NEGOTIABLE # one of: FIXED, NEGOTIABLE, GIVE_AWAY, NOT_APPLICABLE
   shipping_type: SHIPPING # one of: PICKUP, SHIPPING, NOT_APPLICABLE
   # NOTE: shipping_costs and shipping_options must be configured per-ad, not as defaults
-  sell_directly: false # requires shipping_options to take effect
+  sell_directly: false # requires shipping_type SHIPPING to take effect
   contact:
     name: ""
     street: ""
@@ -406,7 +406,7 @@ special_attributes:
   # haus_mieten.zimmer_d: value # Zimmer
 
 shipping_type: # one of: PICKUP, SHIPPING, NOT_APPLICABLE (default: SHIPPING)
-shipping_costs: # e.g. 2.95
+shipping_costs: # e.g. 2.95 (for individual postage, keep shipping_type SHIPPING and leave shipping_options empty)
 
 # specify shipping options / packages
 # it is possible to select multiple packages, but only from one size (S, M, L)!
@@ -423,7 +423,7 @@ shipping_costs: # e.g. 2.95
 # - DHL_31,5
 # - Hermes_L
 shipping_options: []
-sell_directly: # true or false, requires shipping_options to take effect (default: false)
+sell_directly: # true or false, requires shipping_type SHIPPING to take effect (default: false)
 
 # list of wildcard patterns to select images
 # if relative paths are specified, then they are relative to this ad configuration file