feat(tray): add recent dictation snippets history menu 🤖🤖🤖

[LuigiKraken]

Description

Adds a Recent Snippets history menu to the system tray indicator. Each completed dictation session is kept as a snippet; clicking one copies its full text to the clipboard, and a Clear History entry empties the list. This makes it easy to re-paste something you just dictated, or recover earlier input if a paste went wrong.

Key behaviours:

• One snippet per dictation session (everything said between start and stop). Voice commands like "delete that" are not recorded — they go through a separate callback path.
• Recorded on recognition, not on injection success, so text can be recovered even when injection silently no-ops (e.g. on some Wayland compositors). The history is most valuable precisely when a paste/inject goes wrong, so it must not depend on injection succeeding.
• In-memory only — nothing is written to disk; history clears on quit. A deliberate privacy choice for a tool that sees everything the user dictates. (Disk persistence could be added later behind an explicit opt-in.)
• New history config section (enabled, max_items) with a matching Settings → General → Transcription History group (toggle + count).

Implementation notes:

• New vocalinux/ui/transcription_history.py: a small, thread-safe, bounded (deque(maxlen=...)) store with a change-callback. Recording happens on the recognition thread; the tray submenu is rebuilt on the GTK main thread via GLib.idle_add.
• TrayIndicator gains an optional transcription_history= parameter, so existing callers/tests that don't pass it keep working unchanged.

Related Issue

N/A — no existing issue for this; happy to open one to track it if you'd prefer.

Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to change)
• 📖 Documentation update
• 🧹 Code refactoring
• ✅ Test update

Checklist

• My code follows the code style of this project (black, isort)
• I have updated the documentation accordingly (no doc change felt necessary — the feature is discoverable in the tray + Settings; glad to add a README note if you'd like)
• I have added tests to cover my changes (tests/test_transcription_history.py, plus updated tests/test_main.py)
• All new and existing tests pass locally
• Pre-commit hooks pass (black, isort, flake8 --select=E9,F63,F7,F82)

Screenshots (if applicable)

Additional Notes

• Verified live on TUXEDO OS / KDE Plasma (Wayland): snippets record per dictation session, appear newest-first in the tray, and copy to the clipboard on click.
• Opted into the agent-assisted fast-track per CONTRIBUTING.md (🤖🤖🤖 in the title).

[codecov]

Codecov Report

❌ Patch coverage is 94.53125% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.12%. Comparing base (c64b727) to head (cc46eac).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
src/vocalinux/ui/transcription_history.py	94.20%	2 Missing and 2 partials ⚠️
src/vocalinux/main.py	81.81%	0 Missing and 2 partials ⚠️
src/vocalinux/ui/tray_indicator.py	97.91%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #487      +/-   ##
==========================================
+ Coverage   84.72%   85.12%   +0.39%     
==========================================
  Files          31       32       +1     
  Lines        5068     5231     +163     
  Branches      782      807      +25     
==========================================
+ Hits         4294     4453     +159     
- Misses        595      596       +1     
- Partials      179      182       +3     

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