fix(editor): render visible highlight + popover for Flag marks

[vishalsachdev]

Problem

Flagging a selection via the selection bar creates a kind: 'flagged' mark (correctly anchored, saved, and counted by the heatmap gutter) but produces no visible feedback in the document — the decoration pass in createDecorations explicitly skips flagged marks:

case 'authored':
case 'approved':
case 'flagged':
    continue;

Meanwhile STYLES.flagged (the dusty-rose treatment) is defined directly above but never used. From a user's perspective the only observable effect of clicking Flag is the document saving again. Clicking an (invisible) flagged range would also open an empty "Suggestion" popover whose Apply/Reject buttons are no-ops for flagged marks.

Fix

• src/editor/plugins/marks.ts — give 'flagged' its own decoration case (mark-flagged class, wired to the existing STYLES.flagged: 3px rose left border + pale rose background), plus a flag-specific new-mark glow keyframe (box-shadow only, mirroring delete's). Without the dedicated keyframe, the default green glow's forwards fill permanently overrides the rose tint on freshly created flags.
• src/editor/plugins/mark-popover.ts — add a renderFlag() card: "Flagged by {actor}", body shows the flag note (or quoted text), actions are Remove flag (via deleteMark) and Close — replacing the broken empty suggestion popover.

Notes

• The rose visual language is upstream's own dormant STYLES.flagged, just connected; the popover card follows the existing comment-card pattern.
• npm run build clean; test suites pass at parity with baseline on our fork (no new failures). No decoration/DOM-level test harness existed to extend naturally — happy to add one if you can point at a preferred pattern.
• Found while running Proof for real document review; flags created before the fix render correctly after it, since the data layer always worked.

🤖 Generated with Claude Code

https://claude.ai/code/session_01Ro6KiE6zCSSzsqeyVoAu8M