Add privacy-first maintainer trial reports

[Yuki9814]

Why

PatchHive's main growth bottleneck is real external maintainer evidence, not another internal workflow layer. This adds a minimum-disclosure path for voluntary trials without turning PatchHive into a telemetry product.

What changed

• add an optional local maintainer-trial form with fixed-choice answers
• generate one reviewable JSON artifact only after explicit participant consent
• exclude mission content, repository identity, browser identity, and free text
• do not persist or transmit trial answers; sharing remains manual
• clear generated state on import, reset, or recovery so reports cannot cross workspaces
• document the trial protocol, limitations, contribution path, security boundary, and roadmap gate
• keep workspace schema and application version unchanged

Validation

• 143/143 unit tests passed in the complete serial run
• 26/26 privacy performance tests passed
• 14/14 Chromium end-to-end tests passed
• lint, production build, Pages-build verification, dependency audit, and diff checks passed

Evidence boundary

External maintainer trials are still N=0. Generated reports are consented self-reports, not proof of participant independence, and PatchHive makes no adoption claim from this feature alone.