refactor: split ssr.py into package, enrich OG Online detail pages, fix travel upsert

- Split src/adapters/ssr.py (2160 LOC) into ssr/ package grouped by CMS:
  realworks.py, sure.py, schiedam.py, denhaag.py, overige.py
- Add _og_detail() to api.py; all OG Online scrapers now fall back to
  detail page fetch when energielabel/bouwjaar are missing from the API
- Fix run() to recalculate travel times for existing listings where
  fiets_mark IS NULL; upsert() now writes travel cols on existing rows too
- Update tests/cache.py to patch fetch_soup in every ssr submodule
- Update docs to reflect new package structure and mark API enrichment TODO done

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

makelaars.md

@@ -2,7 +2,7 @@
 
 ## TODO
 
-- **API scrapers need detail page enrichment**: OG Online API (bjornd, moerman, vandaal, elzenaar, doen, vandriel) sometimes omits fields like `energyLabel`. We should fetch the detail page for each listing and merge in missing fields (especially energielabel, bouwjaar). This is already done for SSR scrapers; needs to be added to API-based ones.
+- ~~**API scrapers need detail page enrichment**: OG Online API (bjornd, moerman, vandaal, elzenaar, doen, vandriel) sometimes omits fields like `energyLabel`. We should fetch the detail page for each listing and merge in missing fields (especially energielabel, bouwjaar). This is already done for SSR scrapers; needs to be added to API-based ones.~~ ✅ Done — `_og_detail()` added to `api.py`
 
 ## Delft