Interactive block actions using stored transcript ownership #243

Implement the focused v1 block actions designed in #85. Research remains in #85; this child tracks implementation.

Acceptance:

• Shared registry for copy command/output/both, explicit rerun, edit into composer and fold/unfold.
• Keyboard focus and palette reach every action; passive hover/click opens the same action surface.
• Controls hidden by default, right aligned when they fit, and keyboard access retained at narrow widths.
• Shift click/drag never reveal, focus or dispatch; native terminal selection remains authoritative.
• Presenter structural ownership attaches controls to actual command/output rows in Normal and Chat.
• Copy stored plain records, including folded content, without styled-cell scraping or mutation.
• Rerun uses a visible normal shell submission in the current cwd; edit never auto-executes.
• Automated keyboard, Shift suppression, ownership, payload and narrow fallback tests; later physical host QA.

Implementation: #245. Milestone #8. Keep open pending integration and physical QA. Historical inspector browsing, bookmarks/pins, filters and annotations are deferred.