feat(runtime): add browser launch and cache retention options

[olalie]

Summary

Add two optional runtime environment variables:

• TAPMAP_LAUNCH_BROWSER
• TAPMAP_CACHE_RETENTION_MIN

TAPMAP_LAUNCH_BROWSER allows disabling automatic browser launch, making it easier to run TapMap as a background service or via scheduled startup.

TAPMAP_CACHE_RETENTION_MIN automatically removes inactive cached map connections after a configurable number of minutes, reducing map clutter on busy systems while leaving snapshots, reports and Insights unchanged.

Changes

• add LAUNCH_BROWSER and CACHE_RETENTION_MIN configuration options
• add runtime environment variable parsing
• extend RuntimeContext
• make browser launch optional
• add automatic UI cache pruning
• document the new environment variables
• rename runtime test module
• add runtime parser tests
• acknowledge the feature suggestion in the README

Testing

• Manual testing:
  • verified browser launch enabled/disabled
  • verified automatic cache expiration
• Automated:
  • Ruff passes
  • All tests pass (297 passed)