chore(ci): add v8 test coverage tracking (non-blocking baseline)

CI previously ran `pnpm run test || true` — test failures were silently
swallowed with no artifact, so we had no visibility into what was actually
passing across 1,296 test files.

- New `test:coverage` turbo pipeline task + root script; packages that opt
  in by declaring their own `test:coverage` get picked up automatically.
- Wired up three high-value Vitest targets: apps/mana/apps/web (main
  frontend, ~590 tests), shared-ui (Svelte component library), and
  shared-storage (S3 client). Each emits lcov.info + coverage-summary.json
  + browsable HTML.
- apps/mana/apps/web `"test"` was running in watch mode (just `vitest`),
  which hangs under turbo orchestration — changed to `vitest run` and
  added `test:watch` for the interactive case.
- CI uploads coverage artifacts (14-day retention) regardless of whether
  tests passed. `continue-on-error: true` replaces `|| true` so a failed
  suite shows up as a warning annotation on the PR rather than being
  invisible. Flip to a hard gate once main is green for a full week.
- Testing guideline documents the pattern + the template vitest config
  + the planned 80% threshold.
- ESLint flat-config `vitest.config.ts` ignore only matched at the root;
  widened to `**/vitest.config.{ts,js,mjs}` so nested configs don't trip
  the project-service parser.

Coverage baseline produced locally:
  shared-storage:  91.37% lines (6 files, 123 tests)
  shared-ui:        2.87% lines (mostly Svelte components, untested)
  apps/mana/web:    9/59 test files fail — pre-existing, not regression

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/shared-ui/package.json

@@ -45,7 +45,8 @@
 	"scripts": {
 		"lint": "eslint .",
 		"test": "vitest run",
-		"test:watch": "vitest"
+		"test:watch": "vitest",
+		"test:coverage": "vitest run --coverage"
 	},
 	"peerDependencies": {
 		"svelte": "^5.0.0"
@@ -69,6 +70,7 @@
 		"@types/d3-selection": "^3.0.11",
 		"@types/d3-transition": "^3.0.9",
 		"@types/d3-zoom": "^3.0.8",
+		"@vitest/coverage-v8": "^4.1.2",
 		"jsdom": "^29.0.1",
 		"vitest": "^4.1.2"
 	}

packages/shared-ui/vitest.config.ts

@@ -11,6 +11,13 @@ export default defineConfig({
 		clearMocks: true,
 		mockReset: true,
 		restoreMocks: true,
+		coverage: {
+			provider: 'v8',
+			reporter: ['text', 'lcov', 'json-summary'],
+			reportsDirectory: './coverage',
+			include: ['src/**/*.{ts,svelte}'],
+			exclude: ['src/**/*.{test,spec}.{ts,js}', 'src/**/*.d.ts', 'src/test/**', 'src/**/index.ts'],
+		},
 	},
 	resolve: {
 		conditions: ['browser'],