Add editable feedback preview

[mattheliu]

What changed

• adds an inline structured editor for verdict and feedback category
• recomputes the fixed privacy-safe Summary before applying changes
• keeps plugin identity and Host health read-only
• hides the send action while edits are unapplied
• narrows the receipt to 352px and documents the new privacy invariant

Why

Users should be able to correct an Agent-prepared receipt before sending without introducing free text, logs, or task content.

Validation

• pnpm test:all
• 36 client/Host tests and 10 backend tests
• real DSH rc.6 pack/install/boot/remove lifecycle
• real local UI flow: preview → edit → apply → confirm → receipt