fix(web-impl): decouple heartbeat timeouts

[emerardd]

Describe your change

This decouples the FDC3 for Web reference server's heartbeat timings from its open-handler timeout.

• heartbeats: true now uses HeartbeatHandler's existing 5s/30s/60s defaults regardless of openHandlerTimeoutMs.
• Callers can instead pass a HeartbeatOptions object to configure pingInterval, disconnectedAfter, and deadAfter independently.
• The existing boolean API remains compatible, the heartbeat integration fixture now supplies explicit fast test timings, and the change is recorded in the Unreleased changelog.

Related Issue

Resolves #1678.

Contributor License Agreement

• I acknowledge that a contributor license agreement is required and that I have one in place or will seek to put one in place ASAP.

Validation

• npm test --workspace @finos/fdc3-web-impl (109 tests passed, 97.06% coverage)
• ..\..\..\node_modules\.bin\vitest.cmd run test\features\heartbeat.feature (3 tests passed)
• npm run lint --workspace @finos/fdc3-web-impl
• Prettier check on the four changed files
• git diff --check

Review Checklist

• Issue: The related implementation issue is linked above.
• CHANGELOG: An Unreleased CHANGELOG.md entry is included.
• API changes: No FDC3 DesktopAgent, Channel, PrivateChannel, Listener, or Bridging API is changed; this affects only the Web reference implementation server constructor.
• Context types: No Context type schema is created or modified.
• Intents: No Intent is created or modified.

[netlify]

✅ Deploy Preview for fdc3 ready!

Name	Link
🔨 Latest commit	abb13c6
🔍 Latest deploy log	https://app.netlify.com/projects/fdc3/deploys/6a62d7e664a901000886f8cd
😎 Deploy Preview	https://deploy-preview-2030.preview-fdc3.finos.org
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify project configuration.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: Dreamer431 / name: Dreamer431 (abb13c6)

[codecov-commenter]

Codecov Report

❌ Patch coverage is 90.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 95.48%. Comparing base (6fceddc) to head (abb13c6).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
toolbox/fdc3-for-web/fdc3-web-impl/src/index.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #2030    +/-   ##
========================================
  Coverage   95.48%   95.48%            
========================================
  Files          85       85            
  Lines        6705     6712     +7     
  Branches      790     1047   +257     
========================================
+ Hits         6402     6409     +7     
  Misses        303      303            

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.