epic: consistent error handling, notifications and logging #1764

Review of how errors are caught, shown and logged across lib (2026-10-25).

What exists: mapDatabaseError for driver errors (core only), logIgnored for deliberate ignores, toasts, TreeLoadError, QueryErrorView, a startup recovery screen; global handlers in main.dart that only debugPrint.

What is wrong: no persistent log, two logging conventions, about 46 silent empty catches and 46 raw $e messages in lib/features, the same failure surfaced differently on different paths, 301 unawaited calls whose errors only reach the zone handler.

Children

• feat(logging): one log file with rotation, and Open logs / Copy diagnostics in Help #1760: log file with rotation, Open logs and Copy diagnostics
• refactor(errors): one helper that logs an error and tells the user in plain words #1761: one helper that logs and tells the user in plain words
• fix(ui): audit the silent catch blocks in lib/features; some hide failures from the user #1762: audit the silent catch blocks in lib/features
• ci(lint): forbid empty catch blocks in lib/features without logIgnored #1763: lint/ratchet against empty catch

Related: #1757 (failed save of a new connection is reported), #1758, #1759, #1754.