[AZ-359] Refactor C07: collapse RegionService catch ladder via RegionFailureClassifier

Replace 9 nearly-identical catch blocks in
RegionService.ProcessRegionAsync with a single catch (Exception ex)
that delegates to RegionFailureClassifier.Classify, returning a
typed (category, errorMessage) pair. Preserves all original error
messages stored in region summary files; failure-path call into
HandleProcessingFailureAsync is unchanged.

Net source delta: -38 lines in RegionService, +71 lines in new
RegionFailureClassifier (pure static), +10 unit tests covering
each category, precedence, status-code propagation, null guard.

Tests: 68 unit (was 58) + 5 smoke + 3 stub-contract integration
tests pass.

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

_docs/02_tasks/_dependencies_table.md

@@ -36,7 +36,7 @@ Roadmap: `_docs/04_refactoring/03-code-quality-refactoring/analysis/refactoring_
 | AZ-356 | C05 | Stub endpoints return 501 | 1 | — | 2 | Done (In Testing) |
 | AZ-354 | C04 | Strict CORS by default | 1 | — | 2 | Done (In Testing) |
 | AZ-353 | C03 | Sanitize 5xx responses via IExceptionHandler | 1 | — | 3 | Done (In Testing) |
-| AZ-359 | C07 | Consolidate RegionService catch ladder | 2 | — | 3 | To Do |
+| AZ-359 | C07 | Consolidate RegionService catch ladder | 2 | — | 3 | Done (In Testing) |
 | AZ-357 | C06 | Drop tile Version concept; new migration | 2 | — | 5 | To Do |
 | AZ-362 | C09 | Idempotent POST contract | 2 | AZ-353 | 3 | To Do |
 | AZ-366 | C13 | Consolidate Haversine + filename parser | 3 | — | 2 | To Do |