[AZ-370] Refactor C17: status / point-type enums + AC RT2 update

Replaces bare strings with two enums in Common/Enums/:
  RegionStatus { Queued, Processing, Completed, Failed }
  RoutePointType { Start, End, Action, Intermediate }

Adds a Dapper EnumStringTypeHandler<T> (DataAccess/TypeHandlers/)
that round-trips enums to/from lowercase strings, registered once
at startup via DapperEnumTypeHandlers.RegisterAll(). DataAccess now
references Common (project ref) so entities can carry the enum types.

Sites converted: RegionService (5), RouteProcessingService (3),
RoutePointGraphBuilder (4), entity Status/PointType columns. Log
message and summary file format preserved via .ToLowerInvariant().

API JSON contract preserved by adding JsonStringEnumConverter with
JsonNamingPolicy.CamelCase to the http JSON options — single-word
enum members serialize to the same lowercase strings as before.

DTO renamed: Common.DTO.RegionStatus -> RegionStatusResponse to
free the RegionStatus name for the new enum (forced by the task's
explicit enum name); the renamed DTO has no public-API impact at
the JSON wire level. Stale doc references updated.

AC RT2 in _docs/00_problem/acceptance_criteria.md now lists all 4
point types (start/end/action/intermediate).

Tests: 171 / 171 unit + 5 / 5 smoke green (was 141 + 5; +30 new tests
covering type handler round-trip, set/parse, unknown-value rejection,
idempotent registration, and the AC RT2 doc check).

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

_docs/02_document/modules/common_interfaces.md

@@ -13,8 +13,8 @@ Service contracts defining the application's core operations. Implementations li
 - `DownloadAndStoreSingleTileAsync(double latitude, double longitude, int zoomLevel, CancellationToken) → Task<TileMetadata>`: download one tile by lat/lon and persist (added in AZ-311)
 
 ### IRegionService
-- `RequestRegionAsync(Guid id, double lat, double lon, double sizeMeters, int zoomLevel, bool stitchTiles) → Task<RegionStatus>`: creates a region record and enqueues for async processing
-- `GetRegionStatusAsync(Guid id) → Task<RegionStatus?>`: retrieves current status of a region request
+- `RequestRegionAsync(Guid id, double lat, double lon, double sizeMeters, int zoomLevel, bool stitchTiles) → Task<RegionStatusResponse>`: creates a region record and enqueues for async processing
+- `GetRegionStatusAsync(Guid id) → Task<RegionStatusResponse?>`: retrieves current status of a region request
 - `ProcessRegionAsync(Guid id, CancellationToken) → Task`: executes tile downloading, CSV/summary generation, optional stitching
 
 ### IRouteService

_docs/02_document/modules/services_region.md

@@ -6,8 +6,8 @@ End-to-end region processing pipeline: API request handling → queue → backgr
 ## 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`
+- `RequestRegionAsync(...)`: creates `RegionEntity` with status `RegionStatus.Queued`, enqueues a `RegionRequest`, returns `RegionStatusResponse`
+- `GetRegionStatusAsync(Guid id)`: reads region record and maps to `RegionStatusResponse`
 - `ProcessRegionAsync(Guid id, CancellationToken)`: the main processing pipeline — see Internal Logic
 
 ### RegionProcessingService (BackgroundService)
@@ -71,7 +71,7 @@ Each sets status to "failed" and writes an error summary file.
 
 ## Data Models
 - Input: `RegionRequest` (queue message)
-- Output: `RegionStatus` (API response), CSV files, summary files, stitched images
+- Output: `RegionStatusResponse` (API response), CSV files, summary files, stitched images
 - Persistence: `RegionEntity`
 
 ## Configuration