#118 · Inline rollup: render top contributors as proper Signal mentions

Context

The inline rollup output (!rollup non---full) lists contributors as plain text strings: Top answerers: alice (3), Asked by bob. Signal renders these as plain text — no blue highlight, no name tap, no notification to alice/bob that they were credited. Looks half-finished given the codebase's existing UTF-16 mention infrastructure.

Acceptance criteria

• [ ] In handleRollup's inline output (NOT the Outline doc — that path is markdown), build proper Signal mention objects for top_answerers, top_askers, top_link_sharers, etc.
• [ ] Use the existing buildMention() helper at command-handler.ts (search for the function definition — it already handles UTF-16 positioning correctly)
• [ ] Mentions must be properly positioned per the project's UTF-16-not-UTF-8 rule (see CLAUDE.md "Mention Positions" section)
• [ ] Returned CommandResponseWithAttachment should include the mentions: [...] array
• [ ] Test with a name containing emoji (e.g., 📝 alice) to verify offsets are correct

Technical hints

• See command-handler.ts buildMention() and resolveTextMentions() for existing patterns
• The Outline doc path (markdown) is fine as plain text — Signal mentions only apply to in-Signal output
• Top contributors come from the getRollupQAStats/getRollupLinkStats results — they include *_uuid columns to use as mention targets

--- *S-tier (50 pts + 40 = 90). Touches mention building which has an established pattern.*