Add menu bar mode, auto-start tracking, config export/import and UX improvements

[jhodevstuff]

Summary

• Menu bar integration — persistent status icon with tracking controls, dock icon auto-hides when window is closed
• Auto-start tracking — optional setting to begin tracking on app launch
• LoginItemService wired up — "Launch at startup" toggle now actually registers/unregisters the login item
• Config export/import — export settings + people as JSON, import with intelligent people merge (by identifier)
• Unsaved changes warning — amber indicator in settings header when form has uncommitted changes
• Live people name saving — names update on each keystroke instead of requiring Enter

Test plan

• Toggle auto-start tracking, restart app, verify tracking begins automatically
• Close window, verify menu bar icon remains and dock icon disappears
• Use menu bar: start/stop tracking, show window, quit
• Export config, import on fresh install, verify settings and people merge correctly
• Change a setting, verify unsaved changes warning appears, save and verify it clears
• Edit a person's name, verify it persists without pressing Enter