test(e2e): add smoke tests, workflow tests, and Docker integration fixes

[thostetler]

Adds comprehensive e2e test coverage (45 tests) using the Page Object
Model pattern with Playwright running in Docker.

Changes:

• POM base class with session cookie, scenario header, and navigation helpers
• 16 page objects covering all major pages
• Public page smoke tests (home, search, forms, journals DB, auth pages, feedback)
• Protected page smoke tests (libraries, notifications, settings)
• Abstract subpage smoke tests (citations, references, coreads, similar, export)
• Workflow tests: anonymous search, abstract tab navigation, auth-gated nav
• Middleware tests: session bootstrap, auth routing, verify routes
• Stub backend extended with CORS, search/abstract routes, configurable scenarios
• Next.js afterFiles rewrites to proxy client-side API calls in Docker
• Shepherd.js tour suppression via localStorage in test fixture
• ServiceUnavailable component for 5xx errors in abstract pages
• Fix for empty-query facet requests on search page

Depends on PR #807 (POM foundation) — overlapping changes will resolve
once #807 is merged first.

[codecov]

Codecov Report

❌ Patch coverage is 94.44444% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 62.0%. Comparing base (98583b3) to head (e04cd6d).
⚠️ Report is 27 commits behind head on master.

Files with missing lines	Patch %	Lines
src/lib/serverside/absCanonicalization.ts	25.0%	3 Missing ⚠️
...mponents/ServiceUnavailable/ServiceUnavailable.tsx	98.6%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #811     +/-   ##
========================================
+ Coverage    61.7%   62.0%   +0.3%     
========================================
  Files         313     317      +4     
  Lines       36092   36536    +444     
  Branches     1600    1642     +42     
========================================
+ Hits        22237   22618    +381     
- Misses      13818   13881     +63     
  Partials       37      37             

Files with missing lines	Coverage Δ
src/components/SearchFacet/useGetFacetData.ts	77.9% <100.0%> (ø)
...mponents/ServiceUnavailable/ServiceUnavailable.tsx	98.6% <98.6%> (ø)
src/lib/serverside/absCanonicalization.ts	63.6% <25.0%> (+0.5%)	⬆️

... and 18 files with indirect coverage changes

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