perf: fix idle CPU usage, view cascade re-renders, and editor lag

[datlechin]

Summary

Addresses user-reported performance issues: high idle CPU (70°C vs 46°C when closed), general lag, and sluggish editor responsiveness.

Deep codebase audit identified 37 issues. This PR fixes 31 across 22 files:

• NSEvent monitors tied to editor focus — VimKeyInterceptor and InlineSuggestionManager monitors now install/remove on focus/blur instead of running app-wide on every keystroke (P0-1, P0-2)
• Incremental line counting — VimTextBufferAdapter.lineCount uses delta updates instead of O(n) full recount on every text change; setSelectedRange skips needsDisplay when unchanged (P0-3)
• Fine-grained observable counters — Split DatabaseManager.sessionVersion into connectionListVersion/connectionStatusVersion to prevent mass view re-renders on unrelated session changes (P0-4)
• AppState granular tracking — Extract specific AppState properties into local lets so @observable per-property tracking works correctly (P0-5)
• SQL regex windowing — SQLContextAnalyzer now windows text to last 5K chars before running 20+ clause regexes, matching CompletionEngine's existing pattern (P1-1)
• 10K char highlight cap — HighlightedSQLTextView, JSONEditorContentView, AIChatCodeBlockView all cap regex matching range per CLAUDE.md rule (P1-2)
• onChange cascade coalescing — Tab switch onChange uses 16ms Task debounce; merged duplicate handlers (P1-3)
• @bindable scoped to usage site — Moved from struct-level to local variable in queryTabContent() so @observable per-property tracking isn't defeated (P1-6)
• O(1) fuzzy matching — Rewrote fuzzyMatch() to use NSString.character(at:) instead of O(n) String.index(after:) (P1-7)
• DataGrid version tracking — Change reapplication and visual state cache skip work when reloadVersion unchanged (P2-7)
• VoiceOver state cached — Static property with notification observer instead of per-cell system call (P2-4)
• SSH tunnel termination handlers — Process terminationHandler for immediate detection; polling interval 30s → 300s fallback (P2-1)
• onReceive coalescing — TableStructureView merges related notifications with Publishers.Merge + debounce (P2-2)
• Copy pre-allocation — reserveCapacity + direct append instead of intermediate array + joined() (P2-6)
• Teardown guards — Fire-and-forget Tasks check isTearingDown after sleep (P2-10)
• Monitor cleanup consolidation — Idempotent cleanupMonitors() in SQLEditorCoordinator (P2-12)
• KVO cleanup — UpdaterBridge deinit invalidates observation (P2-11)
• Column width optimization — Reduced samples for wide tables, char-count estimation instead of CoreText (P1-5)

Test plan

• Launch app, connect to a database, leave idle for 2+ minutes — verify CPU stays low and temperature doesn't spike
• Open SQL editor, type queries — verify autocomplete is responsive
• Paste a large SQL dump (100KB+) into editor — verify no freeze
• Switch between multiple tabs rapidly — verify no lag
• Enable Vim mode, navigate with hjkl — verify smooth cursor movement
• Open query history with large queries — verify highlighting doesn't freeze
• Connect/disconnect multiple databases — verify sidebar updates without lag
• Select rows, edit cells, save changes — verify DataGrid responsiveness
• Copy 10K+ rows — verify no hang
• Open SSH tunnel connections — verify tunnel health monitoring works

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