fix(provider): capture unknown Claude categories locally

[akoita]

Closes #393

Summary

• add an explicit, disabled-by-default local capture parent for unknown Claude result subtype and terminal-reason categories
• write only bounded category-shaped strings to a new private directory/file while keeping paths and captured values out of errors and run history
• preserve provider classification and retry behavior, with fixed capture-saved/capture-failed diagnostics
• document the diagnostic privacy boundary and roadmap decision

Verification

• pnpm validate
• 103 Vitest files / 1,580 tests passed
• 54 release-script tests passed

The first full gate hit the open #389 intermittent desktop-host mutation failure during portable CKB backup export; that exact test passed 1/1 in isolation, and the unchanged full gate then passed. No provider call was made.