feature: raise unit test coverage to ~98% with Vitest

[devin-ai-integration]

Summary

Adds Vitest unit tests for the ~24 previously-untested source files (interceptors, pipes, the auth directive, layout/shared components, all feature components, and the article/editor/home/profile/settings pages), plus retry/unavailable-state coverage for UserService. No production code was changed.

Coverage (before → after)

Measured with the same vitest.config.ts (all: true over src/**/*.ts, excluding specs, models, routes, app.config.ts, main.ts, test helpers), so the numbers are apples-to-apples.

Metric	Before	After
Statements	18.36%	98.45%
Lines	17.32%	99.5%
Functions	32.66%	98.66%
Branches	5%	89.16%

Tests: 180 → 291 (all passing; no existing tests modified or weakened).

What was tested

• Interceptors: api (url prefixing), token (auth header), error (401 purge, /user special-case, error normalization)
• Pipes: default-image, markdown
• Directive: if-authenticated (view create/clear on auth state)
• Layout/shared: app, header, footer, list-errors
• Article feature: favorite-button, article-meta, article-preview, article-comment, article-list, and the article, editor, home pages
• Profile feature: follow-button, profile-articles, profile-favorites, and the profile page
• Settings: settings page
• UserService: added 5XX retry/backoff + unavailable state + retry-cancel tests (70.9% → 98.18%)

Notes / mechanics

• Added @vitest/coverage-v8 and zone.js dev deps (required for v8 coverage + Angular TestBed in jsdom).
• New shared helper src/testing/setup-test-bed.ts initializes the Angular TestBed once per file (imports @angular/compiler first to avoid JIT errors on PlatformLocation). Excluded from coverage.
• vitest.config.ts: enabled all: true so untested files count toward overall coverage, added json-summary reporter, and excluded non-executable declaration/config files (models, routes, app.config.ts).
• Components are tested by injecting them via TestBed with mocked services (RxJS of/throwError/BehaviorSubject); HTTP-level service tests keep using HttpClientTestingModule.
• Ran bun run format; format:check is clean. e2e/Playwright tests untouched.

Link to Devin session: https://app.devin.ai/sessions/54747daa1bc44e1187c3da73f91a8489
Requested by: @bnob-git

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[devin-ai-integration]

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[devin-ai-integration]

CI note: test (Playwright e2e) failure is pre-existing and unrelated to this PR

This PR only adds unit tests + Vitest coverage config/deps; it changes no production code. The test CI job runs bun run test:e2e (Playwright), not the unit tests — unit tests aren't run in CI.

The 6 failures are all in e2e/settings.spec.ts ("Settings - Profile Updates"), where the settings update API returns 422 in the no-API mode the repo runs e2e under (so the page stays on /settings instead of redirecting to /profile/...).

I reproduced this on a clean checkout of the base branch (main, f39866e):

$ bun run test:e2e -- e2e/settings.spec.ts   # on origin/main
  6 failed
  1 passed (2.0m)

Identical 6 failures → these are pre-existing on main, independent of this PR. format and security-tests checks pass.