feat: show default session notes persistently

[ushmz]

Summary

Added show_default_notes configuration option to display default session notes persistently in the background when no named session or retrace mode is active.

Key features:

• Default session notes are always visible when working without an explicit session
• Automatically hidden when starting a named session or entering retrace mode
• Automatically restored when ending a session or exiting retrace mode
• Configurable via show_default_notes option (default: true)

Changes

Configuration

• lua/tabi/config.lua: Added show_default_notes option (default: true)

Core Implementation

• lua/tabi/init.lua:
  • Added _setup_default_session_display() to setup background display
  • Added _clear_default_session_display() to cleanup autocmds
  • VimEnter autocmd to initialize display on startup

Integration

• plugin/tabi.lua:

  • Session start: Clear default display
  • Session end: Restore default display

• lua/tabi/retrace.lua:

  • Retrace start: Clear default display
  • Retrace end: Restore default display

Tests

• test/tabi/config_spec.lua: Config tests (3 cases)
• test/tabi/integration/default_session_display_spec.lua: Comprehensive integration tests (16 cases)
  • Startup behavior
  • Session lifecycle integration
  • Retrace mode integration
  • Autocmd management
  • Complex scenarios

Behavior

When show_default_notes: true (default):

Startup → Show default session notes
↓
Start named session → Hide default, show session notes
↓
End session → Restore default notes
↓
Start retrace → Hide default, show retrace notes
↓
End retrace → Restore default notes

When show_default_notes: false:

• No background display of default session
• Traditional behavior (only show notes in active sessions)

Test plan

• All 386 tests pass (364 existing + 22 new)
• luacheck and stylua checks pass
• Config option works correctly
• Display toggles properly on session/retrace start/end
• Autocmds are properly managed (no leaks)
• Feature can be disabled via config