* fix(ai-insights): keep usage snapshots out of process arguments

Use private one-use snapshot files between QML and the packaged helper, with ownership checks and cleanup before AI or wallet activity. Exercise the actual handoff and process command lines. Update usage, implementation and requirements docs, and record the separate account-selector CLI limitation in TODO.

* fix(ai-insights): avoid deprecated Qt snapshot encoding

Encode the bounded ASCII snapshot as hexadecimal in the pure policy module. This preserves the private file handoff across Qt versions and removes Qt 6.11's Qt.btoa(string) warning without weakening warning assertions. Update the reader, bounds, tests and handoff documentation.

* fix(ai-insights): type the private input settings instance

Cast the dynamically created QObject to QtCore.Settings before calling setValue and sync, so the strict CI QML type check can validate those methods. Retain the existing null guard and private-file lifecycle.

Documentation, TODO, catalogs and the Unreleased entry remain accurate; there is no behavior or interface change.

* fix(ai-insights): prefer validated private runtime storage

Use XDG_RUNTIME_DIR only when it is an existing absolute directory owned by the current user with no group/other access. Preserve the fail-closed temporary fallback without modifying unsafe existing roots.

Cover runtime selection and temporary-root collision handling, isolate runtime storage in controller/smoke fixtures, and document the remaining fallback availability limitation. Existing usage, requirements, Unreleased entry and TODO remain accurate.