feat(harness): agent-drivable dev harness and CI that gates

A coding agent could develop this repo's Go packages and could not
develop the application: every path to running YellowJacket ended in a
blocking GTK window, so 265 bound methods, 46 events, 33 component
directories and 13 stores had exactly one form of verification
available — `tsc --noEmit`.

The unlock is that `wails dev`'s dev server on :34115 serves the real
frontend with the real generated bindings against the same Go backend a
desktop window attaches to, so a plain Chromium under Xvfb gets a fully
functional app. Four test tiers now exist, cheapest first:

- `make ui-test` — 313 Vitest tests in a real browser in ~2 s, no app,
  no backend, no display. Works because `frontend/wailsjs/` is a pure
  passthrough to `window.go`/`window.runtime`, so faking just those two
  globals runs the real bindings and the real store code.
- `make test` — services in-process, asserting on the payload the
  frontend would receive, via a new `events.Emit` wrapper.
- `make dev-headless` + `playwright-cli` — the real app, driven
  interactively, with an event bridge on `window.__yjEvents` and a
  dev-only control surface at `/__test/`.
- `make e2e` — 19 of those flows frozen as Playwright specs.

`events.Emit(ctx, …)` replaces all 35 direct `runtime.EventsEmit` call
sites: wails' `getEvents` `log.Fatalf`s on any context without its
runtime, so those paths could not run under test and a background
worker could take the app down. Four packages had each hand-rolled the
same guard; nine more guarded on `ctx != nil`, which does not help.
`TestNoDirectRuntimeEmits` fails the build on a new one.

Fixtures are generated, not committed (`make testdata`), and seeds are
built by *running the app* — never by hand-writing config and DB rows,
which would be a second description of a valid YJ_HOME.

`.gitea/workflows/ci.yml` is the first workflow here that tests
anything; the other three only package, so `gitea_ci` reported only
packaging jobs and misled anyone asking whether a push was healthy.
Both jobs were prototyped to green in a bare ubuntu:24.04 container
before the YAML was written, which immediately caught `make lint`
linting three configurations that nothing builds: all three passes
omitted `webkit2_41`, so wails resolved webkit2gtk-4.0 — which Arch
still ships and Ubuntu 24.04 dropped.

Operational instructions live in `.pi/skills/yellowjacket-dev/`,
measured discoveries in `.planning/NOTES.md`, and architecture in
`CLAUDE.md` — split by tense, not by topic, because a topical split
gives every new fact two plausible homes. `make skill-check` fails a
commit if the skill cites a make target that does not exist.

backend/metadata/flacduration_test.go

@@ -4,40 +4,32 @@ import (
 	"os"
 	"path/filepath"
 	"testing"
+
+	"yellowjacket/internal/testfixtures"
 )
 
-// testFlacFiles returns the paths to all .flac files in the
-// test_data directory.  It skips the test if none are found.
+// testFlacFiles returns every .flac in the generated fixture library
+// (`make testdata`).
+//
+// Sourced from the manifest rather than by walking test_data/, which
+// used to sweep up the deliberately malformed fixtures — a zero-byte
+// .flac is there to prove the scanner survives it, not to be handed to
+// a duration parser.
 func testFlacFiles(t *testing.T) []string {
 	t.Helper()
 
-	root := filepath.Join("..", "..", "test_data")
-
-	if _, err := os.Stat(root); os.IsNotExist(err) {
-		t.Skip("test_data directory not present, skipping")
-	}
+	m := testfixtures.Load(t)
 
 	var files []string
 
-	err := filepath.Walk(root, func(
-		path string, info os.FileInfo, err error,
-	) error {
-		if err != nil {
-			return err
+	for _, track := range m.Tracks {
+		if track.Format == "flac" {
+			files = append(files, m.Abs(track.Path))
 		}
-
-		if !info.IsDir() && filepath.Ext(path) == ".flac" {
-			files = append(files, path)
-		}
-
-		return nil
-	})
-	if err != nil {
-		t.Fatalf("walking test_data: %v", err)
 	}
 
 	if len(files) == 0 {
-		t.Skip("no .flac test fixtures found in test_data/")
+		t.Skip("no .flac fixtures in the manifest")
 	}
 
 	return files

backend/metadata/mp3duration_test.go

@@ -4,44 +4,30 @@ import (
 	"os"
 	"path/filepath"
 	"testing"
+
+	"yellowjacket/internal/testfixtures"
 )
 
-// testMP3Files returns the paths to all .mp3 files in the curated
-// fixture library (`test_data/music_library_test/`).  Scoped
-// narrowly so that ad-hoc scramble / autotag fixtures placed
-// elsewhere under `test_data/` (e.g. `test_data/mb-tag/`) don't
-// get pulled into the assertion and fail on non-curated codecs.
-// Skips the test when the directory isn't present.
+// testMP3Files returns every .mp3 in the generated fixture library
+// (`make testdata`).  Scoped to that manifest so ad-hoc scramble /
+// autotag fixtures elsewhere under `test_data/` don't get pulled into
+// the assertion and fail on non-curated codecs.  Skips when the
+// fixtures haven't been generated.
 func testMP3Files(t *testing.T) []string {
 	t.Helper()
 
-	root := filepath.Join("..", "..", "test_data", "music_library_test")
-
-	if _, err := os.Stat(root); os.IsNotExist(err) {
-		t.Skip("test_data/music_library_test not present, skipping")
-	}
+	m := testfixtures.Load(t)
 
 	var files []string
 
-	err := filepath.Walk(root, func(
-		path string, info os.FileInfo, err error,
-	) error {
-		if err != nil {
-			return err
+	for _, track := range m.Tracks {
+		if track.Format == "mp3" {
+			files = append(files, m.Abs(track.Path))
 		}
-
-		if !info.IsDir() && filepath.Ext(path) == ".mp3" {
-			files = append(files, path)
-		}
-
-		return nil
-	})
-	if err != nil {
-		t.Fatalf("walking test_data: %v", err)
 	}
 
 	if len(files) == 0 {
-		t.Skip("no .mp3 test fixtures found in test_data/")
+		t.Skip("no .mp3 fixtures in the manifest")
 	}
 
 	return files