test(frontend): add vitest suite mirroring backend coverage

[xishell]

Summary

Brings the frontend up to backend test parity: a Vitest suite with shared fixtures, factories, and a coverage gate at 80%, plus a CI job that posts the coverage report on every PR.

Changes

• Add Vitest suite under src/**/__tests__/: 117 tests across pages,
  components, hooks, and lib helpers. Mirrors the backend layout where
  every router has a test_*_api.py.
• New shared fixtures in src/test/, setup.ts (jsdom + in-memory
  Web Storage shim that survives node 22's experimental localStorage),
  helpers.tsx (renderWithAuthLayout, mockFetch, factories), and
  eventSource.ts (FakeEventSource for SSE-driven hooks).
• Wire @vitest/coverage-v8 with thresholds lines/statements/functions = 80,
  branches = 75. Local: bun run test:cov.
• Add frontend-vitest job in .github/workflows/test.yml using
  davelosert/vitest-coverage-report-action, posting a coverage comment
  on PRs and a step summary on every run.

Checklist

• Code compiles/builds without errors or warnings
• Code follows the project style guide and has been formatted
• All existing tests pass
• New functionality includes appropriate tests
• PR title follows Conventional Commits format

[github-actions]

Coverage Report for Frontend coverage (frontend)

Status	Category	Percentage	Covered / Total
🔵	Lines	91.25% (🎯 80%)	584 / 640
🔵	Statements	88.48% (🎯 80%)	630 / 712
🔵	Functions	86.09% (🎯 80%)	161 / 187
🔵	Branches	78.97% (🎯 75%)	387 / 490

File Coverage

No changed files found.

Generated in workflow #208 for commit 1c46087 by the Vitest Coverage Report Action

[github-actions]

Backend coverage

File	Stmts	Miss	Cover	Missing
app
__init__.py	1	0	100%
auth.py	26	2	92%	40–41
broadcaster.py	23	2	91%	18–19
config.py	19	0	100%
db.py	15	4	73%	20, 31, 35–36
dependencies.py	13	0	100%
events.py	74	3	96%	62–63, 71
logging_config.py	91	43	53%	17, 24–27, 32–33, 38–47, 58–61, 78–130
main.py	93	28	70%	77–81, 86–97, 107–116, 170–180
models.py	128	0	100%
mqtt.py	151	68	55%	36, 40–48, 117–118, 158–183, 199–206, 218–231, 236–273
notifications.py	25	1	96%	52
schemas.py	158	0	100%
app/adoption
__init__.py	0	0	100%
claims.py	36	0	100%
finalize.py	49	1	98%	101
sweeper.py	31	11	65%	41–51
app/routers
adoptions.py	100	16	84%	35–36, 171–184
auth.py	41	1	98%	68
berths.py	73	13	82%	34, 61–72, 160
docks.py	22	11	50%	22–26, 36–46
gateways.py	18	0	100%
harbors.py	11	0	100%
nodes.py	71	2	97%	74, 79
users.py	53	1	98%	87
TOTAL	1322	207	84%

Tests	Skipped	Failures	Errors	Time
156	0	0	0	11.170s