chore(types): enable strictNullChecks in base config with explicit null guards in server/config/core [WPB-23695]

[screendriver]

WPB-23695 [Web] Enable strict TypeScript mode

Pull Request

Summary

• enable strictNullChecks in base TypeScript config
• fix strict-null regressions in server, config-lib, and core-lib with explicit null/undefined checks (no implicit truthy/falsy checks in touched code)
• improve unhandled rejection type logging with explicit type narrowing
• add/update tests for new null-handling behavior:
  • client build date parsing when version is missing
  • server config defaults when URLs are missing
  • link preview audit upload with missing title
  • browser util test helper null safety
• keep webapp temporarily opted out via local strictNullChecks: false override due to existing nullability backlog and unresolved module typing in webapp:type-check

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Security Checklist (required)

• External inputs are validated & sanitized on client and/or server where applicable.
• API responses are validated; unexpected shapes are handled safely (fallbacks or errors).
• No unsafe HTML is rendered; if unavoidable, sanitization is applied and documented where it happens.
• Injection risks (XSS/SQL/command) are prevented via safe APIs and/or escaping.

Accessibility (required)

• I have read and this PR upholds our Accessibility Best Practices.

Standards Acknowledgement (required)

• I have read and this PR upholds our Coding Standards and Tech Radar Choices.

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Screenshots or demo (if the user interface changed)

Notes for reviewers

• Trade-offs:
• Follow-ups (linked issues):
• Linked PRs (e.g. web-packages):

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 45.40%. Comparing base (2b43bae) to head (9b58ce8).
⚠️ Report is 1 commits behind head on dev.

Files with missing lines	Patch %	Lines
...braries/core/src/linkPreview/LinkPreviewService.ts	50.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev   #20510      +/-   ##
==========================================
+ Coverage   45.38%   45.40%   +0.01%     
==========================================
  Files        1637     1637              
  Lines       40363    40364       +1     
  Branches     8333     8334       +1     
==========================================
+ Hits        18319    18326       +7     
+ Misses      20108    20101       -7     
- Partials     1936     1937       +1     

Flag	Coverage Δ
app_webapp	43.59% <ø> (ø)
lib_api_client	50.17% <ø> (ø)
lib_core	59.05% <50.00%> (+0.18%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...braries/core/src/linkPreview/LinkPreviewService.ts	75.00% <50.00%> (+56.81%)	⬆️

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[github-actions]

🔗 Download Full Report Artifact

🧪 Playwright Test Summary

• ✅ Passed: 10
• ❌ Failed: 0
• ⏭ Skipped: 4
• 🔁 Flaky: 0
• 📊 Total: 14
• ⏱ Total Runtime: 84.9s (~ 1 min 25 sec)

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud