feat(calendar): opt-in durable UUID recovery for private Google Calendar projections

[martin-forge]

Problem

Google task events can go missing, duplicate, or link to an old path after task files move or the local event index is lost. A damaged or missing task file must not make recovery delete its Calendar event.

Solution

Add an optional Rebuild private task projections setting, off by default. Exported tasks receive a persistent UUID. Startup and the existing recovery loop use it to repair event links, missing events and stale details.

Cleanup requires a readable task with the same UUID and either a retirement marker or an identical surviving event. Missing IDs and unreadable files preserve events. The same check protects queued retries, and deletion refuses a provider revision that changed after verification. Unrelated and invited events remain untouched.

Testing

• 30 recovery and provider-safety tests pass, including damaged files, retries, retirement, differing duplicate content and changed provider revisions.
• Lint and build:test pass. Live Obsidian checks against disposable Google events confirm that malformed frontmatter and missing task IDs preserve the events.
• Two local filtering/locale failures also reproduce on the unchanged parent branch.
• GitHub CI passed: tests, lint, type checks and build.