feat: smart value display formats (UUID, timestamps)

[datlechin]

Summary

Closes #625.

• Auto-detect UUIDs in BINARY(16)/VARCHAR(36) columns and Unix timestamps in INT/BIGINT columns
• Per-column "Display As" override via column header right-click menu (persisted per connection+table)
• Global "Smart value detection" toggle in Data Grid settings (on by default)
• Formatted values shown in grid, inspector sidebar, and cell copy; SQL export uses raw values

No competitor does auto-detection — DBeaver, DataGrip, Sequel Ace all require manual per-column configuration.

Detection heuristics (conservative — requires both type + name match):

• UUID: BINARY(16) columns where name contains "uuid", "guid", or "_id". CHAR/VARCHAR(32/36) where name contains "uuid"/"guid"
• Unix timestamp: INT/BIGINT columns where name ends with _at, _time, _timestamp, or equals created/updated/modified/timestamp. Sample value validated in 2000-2099 range. Values >10B auto-detected as milliseconds

New files

• ValueDisplayFormat.swift — enum (raw, uuid, unixTimestamp, unixTimestampMillis)
• ValueDisplayDetector.swift — heuristic auto-detection engine
• ValueDisplayFormatService.swift — format application + resolution (override > auto > raw)
• ValueDisplayFormatStorage.swift — UserDefaults persistence per connection+table

Modified files

• CellDisplayFormatter.swift — new displayFormat parameter, applied before date/blob formatting
• RowProvider.swift — stores columnDisplayFormats, passes to formatter
• AppSettings.swift / DataGridSettingsView.swift — enableSmartValueDetection toggle
• DataGridView+Sort.swift — "Display As" submenu in column header context menu
• DataGridCoordinator.swift — settings change observer for smart detection toggle
• DataGridView+RowActions.swift — copy cell uses formatted value when format active
• MainContentView+Bindings.swift — sidebar applies display format
• MainEditorContentView.swift — wires up auto-detection on row provider creation

Test plan

• Connect to MySQL with BINARY(16) UUID column (name containing "uuid"/"id") → verify auto-renders as UUID
• Connect to any DB with INT created_at column → verify shows human-readable date
• Right-click column header → "Display As" → switch between formats, verify checkmark updates
• Override persists after re-opening the table
• Toggle "Smart value detection" off in Settings → auto-detection stops, overrides still work
• Copy cell with UUID format → clipboard has UUID string
• Copy as INSERT → raw binary value used (not UUID string)
• Multiple connections open simultaneously → formats don't cross-contaminate
• Query tab (no table) → auto-detection works, "Display As" menu works (non-persisted)