v0.5.0

v0.5.0: export open tabs to CSV

- src/tabexport.py: on-demand snapshot of every open tab across running
  browsers -> CSV (browser, window, tab, active, pinned, loading, window_mode,
  last_accessed, title, url). Safari/Chromium via AppleScript, Firefox via the
  session file. Read-only, local, nothing persisted; private windows excluded.
- app.py: 'Export open tabs to CSV…' menu item -> re-poll -> gather -> native
  Save panel (app-name + timestamp filename) -> reveal in Finder.
- FIX: force UTF-8 decoding in tabcount._osascript. A py2app app launched from
  Finder runs under a C/POSIX locale, so subprocess text mode defaulted to ASCII
  and crashed on non-ASCII tab titles (em dashes, ellipses, emoji). Reproduced
  and fixed; also hardens counting. _osascript gains a timeout arg (export=20s).
- tests/test_tabexport.py; README documents the feature; version -> 0.5.0.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>