Guard user data from registered files, dashboards and apps; per-tab r…

[JetSquirrel]

…esults

• re-attaching a registered file never replaces a table or view the user made: DuckLocal tags what it creates with a catalog comment and reports a name clash instead of CREATE OR REPLACE over the user's relation
• .dash queries must be one read-only statement (DuckDB's own json_serialize_sql judgement, PIVOT allowed); the GUI refuses anything else before it runs, and check/lsp report it as a diagnostic
• an app folder asks "Trust and run" once before any of its code or SQL runs; the answer is remembered per folder in settings
• each query tab owns its results panel, and a run lands in the tab that started it, so export uses that tab's SQL
• non-UTF-8 command-line paths no longer panic the GUI launch
• docs and skill updated for the dashboard and app rules