docs: one-click capture, retries, and on-page notice

[DCCA]

Documentation-only follow-up for the one-click capture work and its reliability/notice hardening (#8, #11–#14).

• CLAUDE.md: updated the architecture to reflect the removed popup + onClicked handler, the full content.ts message set (incl. SB_CAPTURE_BEGIN/SB_SET_OVERLAY/SB_CAPTURE_END), the capture.ts retry helpers/guards (activateTab, sendToContentScript, isTabsBusyError, isNoReceiverError), the on-page notice flow (double-rAF paint guarantee), and the wslPath/feedback helpers in the unit-tested list.
• README: added one-click capture, the capture notice, and Copy for Claude Code to the features.
• .docs/todo: removed the now-nonexistent popup from the manual QA list; added one-click + notice QA items.
• .docs/done/2026-06-27-one-click-capture-reliability/: FIREHOSE change record (proposal/spec/design/tasks/completion-summary) for PRs fix(capture): retry content-script message on one-click auto-capture #11–fix(capture): keep the capture notice out of the screenshot #14.

No code change.

Verification

• npm run check green on main before branching; format:check clean (CLAUDE.md/README prettier-clean, .docs/ is prettier-ignored).
• Dogfooded dist/: manifest has no popup + downloads permission; content.js carries the notice + double-rAF; editor.js carries the retry guards.

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