[AZ-284] Autodev baseline + testability refactor

Phase A baseline outputs from /autodev (Steps 1-5):
- Problem & solution docs (_docs/00_problem, _docs/01_solution)
- Codebase documentation (_docs/02_document) incl. architecture,
  module-layout, glossary, system-flows, baseline compliance scan
- Test specs (blackbox, performance, resilience, security, resource,
  traceability matrix)
- Test task decomposition (_docs/02_tasks/todo): AZ-285..AZ-290
- Testability refactor (_docs/04_refactoring/01-testability-refactoring):
  - TC-01 Move DownloadedTileInfoV2 + new ExistingTileInfo to Common.DTO
  - TC-02 Replace dead ISatelliteDownloader API with real signatures
  - TC-03 GoogleMapsDownloaderV2 implements ISatelliteDownloader
  - TC-04 TileService depends on ISatelliteDownloader (mockable)
  - TC-05 DI + endpoints use ISatelliteDownloader
- Test runner scripts (scripts/run-tests.sh, run-performance-tests.sh)
- Autodev state pointer (_docs/_autodev_state.md)

Prepares the codebase for AZ-285..AZ-290 unit/integration test work.

Co-authored-by: Cursor <cursoragent@cursor.com>

_docs/02_document/modules/services_region.md

@@ -0,0 +1,91 @@
+# Module: Services/RegionService + RegionProcessingService + RegionRequestQueue
+
+## Purpose
+End-to-end region processing pipeline: API request handling → queue → background worker → tile download → output file generation. Three closely coupled classes form the region processing subsystem.
+
+## Public Interface
+
+### RegionService (implements IRegionService)
+- `RequestRegionAsync(...)`: creates `RegionEntity` with status "queued", enqueues a `RegionRequest`, returns `RegionStatus`
+- `GetRegionStatusAsync(Guid id)`: reads region record and maps to `RegionStatus`
+- `ProcessRegionAsync(Guid id, CancellationToken)`: the main processing pipeline — see Internal Logic
+
+### RegionProcessingService (BackgroundService)
+- `ExecuteAsync(CancellationToken)`: spawns `MaxConcurrentRegions` parallel worker tasks, each in an infinite dequeue loop
+
+### RegionRequestQueue (implements IRegionRequestQueue)
+- `EnqueueAsync(RegionRequest, CancellationToken)`: writes to a bounded `Channel<RegionRequest>`
+- `DequeueAsync(CancellationToken)`: reads from the channel (blocks until available)
+- `Count`: current queue depth
+
+## Internal Logic
+
+### RegionService.ProcessRegionAsync
+1. Sets region status to "processing"
+2. Creates a 5-minute timeout `CancellationTokenSource`
+3. Queries existing tiles in the region
+4. Calls `TileService.DownloadAndStoreTilesAsync` to fetch missing tiles
+5. Counts downloaded vs reused tiles
+6. Generates CSV file (`region_{id}_ready.csv`) listing tile coordinates + paths
+7. Optionally stitches tiles into a single JPEG image (if `StitchTiles` is true)
+8. Generates summary file (`region_{id}_summary.txt`)
+9. Updates region status to "completed"
+10. On any error: sets status to "failed", generates error summary
+
+### Tile Stitching
+Uses ImageSharp to:
+1. Compute a tile grid from tile coordinates
+2. Create a new image of `(gridWidth × 256) × (gridHeight × 256)` pixels
+3. Place each tile image at its grid position
+4. Draw a red crosshair at the center coordinates
+5. Save as JPEG
+
+### Error Handling
+Comprehensive catch blocks for:
+- `TaskCanceledException` (timeout vs external cancellation)
+- `OperationCanceledException`
+- `RateLimitException` (Google rate limiting)
+- `HttpRequestException` (with status code)
+- Generic `Exception`
+Each sets status to "failed" and writes an error summary file.
+
+### RegionProcessingService
+- Spawns `MaxConcurrentRegions` worker tasks with staggered startup (100–500ms random delay)
+- Each worker loops: dequeue → `ProcessRegionAsync` → repeat
+- Graceful shutdown on cancellation
+
+### RegionRequestQueue
+- Uses `System.Threading.Channels.Channel<T>.CreateBounded` with `BoundedChannelFullMode.Wait`
+- Tracks `_totalEnqueued` and `_totalDequeued` counters
+
+## Dependencies
+- `ITileService`, `IRegionRepository`, `IRegionRequestQueue`
+- `StorageConfig`, `ProcessingConfig`
+- `SixLabors.ImageSharp` — tile stitching
+- `SatelliteProvider.Common.Utils.GeoUtils` — coordinate conversion for stitching
+
+## Consumers
+- `Program.cs` API endpoints — `RequestRegionAsync`, `GetRegionStatusAsync`
+- `RouteService` — `RequestRegionAsync` (for geofence regions)
+- `RouteProcessingService` — `RequestRegionAsync` (for route-point regions)
+
+## Data Models
+- Input: `RegionRequest` (queue message)
+- Output: `RegionStatus` (API response), CSV files, summary files, stitched images
+- Persistence: `RegionEntity`
+
+## Configuration
+- `StorageConfig.ReadyDirectory` — output file location
+- `ProcessingConfig.MaxConcurrentRegions` — worker count
+- `ProcessingConfig.QueueCapacity` — bounded channel size
+
+## External Integrations
+- PostgreSQL (via repositories)
+- File system (CSV, summary, stitched images in `./ready/`)
+- Google Maps (indirectly via TileService → GoogleMapsDownloaderV2)
+
+## Security
+None.
+
+## Tests
+Integration tests in `RegionTests.cs` cover the request → poll → complete flow.