fix(264): log local path scan errors (review finding) + map Scanner.Tests

Adversarial review (MERGEABLE, no blockers) raised two items worth
folding in rather than deferring:

Medium — ScanLocalLibraryHandler silently swallowed path scan errors,
while the three remote scanners it mirrors all log result.LeftToSeq().
That mattered less when a failed path only skipped the path-level
LastScan, but the previous commit makes a failed path suppress the
library-level scan time too — so the user would see exactly the #264
symptom ("Never scanned") with nothing in the log explaining why. That
is a diagnosis dead-end of the same class as the bug being fixed, so
log it here rather than file a follow-up. No test: the sibling
Synchronize*LibraryByIdHandlerTests don't assert on logging either, and
LogError is an extension method that NSubstitute can't cleanly verify.

Low — docs/testing.md bills itself as the authoritative map of what each
test project covers but omitted ErsatzTV.Scanner.Tests entirely (1471
pre-existing tests). This PR adds a file to that project, so add the row
and include it in the per-PR verification gate.

ErsatzTV.Scanner/Application/MediaSources/Commands/ScanLocalLibraryHandler.cs

@@ -149,6 +149,17 @@ public class ScanLocalLibraryHandler : IRequestHandler<ScanLocalLibrary, Either<
                 else
                 {
                     anyFailed = true;
+
+                    // a failed path now suppresses the library-level scan time below, so without this the
+                    // user sees "Never scanned" with nothing explaining why. The remote scanners log the
+                    // same way.
+                    foreach (BaseError error in result.LeftToSeq())
+                    {
+                        _logger.LogError(
+                            "Error scanning local library path {Path}: {Error}",
+                            libraryPath.Path,
+                            error);
+                    }
                 }
             }
 

docs/testing.md

@@ -9,6 +9,7 @@ before adding tests, not just `docs/contributing.md` §8 (which now just points
 |---|---|---|
 | `ErsatzTV.Tests` | API controllers + MediatR handlers | In-memory SQLite fixture: a shared `SqliteConnection("Data Source=:memory:;Foreign Keys=False")` kept open + `EnsureCreatedAsync()` (**not** full migration replay) + `PRAGMA foreign_keys=OFF`, then seed; a tiny `IDbContextFactory` wraps `new TvContext(...)`. 828 tests currently. |
 | `ErsatzTV.Core.Tests` | Domain logic, scheduling, IPTV/XMLTV generation | References `ErsatzTV.Application` directly — there is no separate `Application.Tests` project. 542 tests + 1 skipped under `TZ=UTC` (the Block playout golden additionally skips under a non-UTC `TZ`; see Golden-file nets). |
+| `ErsatzTV.Scanner.Tests` | Library scanning: scan handlers, folder scanners, NFO readers | Handler tests substitute the folder scanners + `ILibraryRepository` and assert the resulting repository writes (e.g. `ScanLocalLibraryHandlerTests` pins which `LastScan` levels a scan records — ersatztv#264). Fakes/`Testably` back the file-system-facing scanners. 1471 tests. |
 | `ErsatzTV.Architecture.Tests` | Layering rules via NetArchTest.eNhancedEdition | Core↛Infra/App/EF; FFmpeg↛all; App↛concrete providers. 5 tests. See `docs/contributing.md` §1. |
 | `ErsatzTV.FFmpeg.Tests` | FFmpeg command construction | Build a pipeline, assert the exact rendered arg string (`PipelineBuilderBaseTests.cs`). |
 | `web/` (vitest) | React SPA unit tests | 330 tests; run alongside typecheck + build (see below). |
@@ -86,7 +87,7 @@ npm run build      # tsc -b && vite build
 ## Per-PR verification gate
 
 Before opening a PR: build the solution, run both .NET test projects (plus
-`ErsatzTV.Architecture.Tests` and `ErsatzTV.FFmpeg.Tests` if touched), and run the web test/lint/
+`ErsatzTV.Scanner.Tests`, `ErsatzTV.Architecture.Tests` and `ErsatzTV.FFmpeg.Tests` if touched), and run the web test/lint/
 typecheck/build steps above. All must be green. A golden-file diff or an architecture-test
 failure is a hard stop — fix the code, don't regenerate/relax the test.