feat: 6738 enforce geospatial upload and preview limits

[ihar-tsykala]

Description:

Large geospatial files could freeze the browser or fail without a useful message. KML and KMZ were not handled consistently, the original upload was lost after conversion to GeoJSON, and the server did not enforce the browser's limits.

This change adds shared configurable limits for GeoJSON, KML and KMZ. Files above the preview limit can be stored without rendering, while files above the maximum are rejected. The original file is kept in IndexedDB before submit and in GridFS and IPFS afterwards. GeoJSON and KML use lossless gzip storage, KMZ remains unchanged, and downloads return the original bytes. Server validation checks the real stored content of every link inside a GeoJSON value and logs rejections and accepted no-preview uploads. If a draft is opened where its file is not available, the field asks to import it again. A failed upload before submit is rolled back for tables and geo files alike. The IPFS transformation addon passes the stored geo file to external systems as a link or base64, the same way it passes table files. Existing documents without a file link, and forms without geo files, continue to work as before.

The common cross-service upload transport is deliberately unchanged. Its JSON expansion for large files remains tracked separately.

Fixes #6738

Checklist

• Documented (Code comments, README, etc.)
• Tested (unit, integration, etc.)

[github-actions]

Test Results

 33 files  ±0   66 suites  ±0   3m 16s ⏱️ +4s
 35 tests ±0   35 ✅ ±0  0 💤 ±0  0 ❌ ±0 
173 runs  ±0  173 ✅ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit 608f5c0. ± Comparison against base commit 50a4188.

♻️ This comment has been updated with latest results.