fix: bound and polish thread expansion

[douglasmonsky]

Summary

• load only the first 100 aggregate calls when a thread expands, with explicit 100-call pagination
• replace the unfinished native-looking Threads grid with a compact scan-first layout and aligned sortable headers
• keep advanced metrics available through Columns while improving truncation, placeholders, sticky identity, and mobile behavior

Verification

• full dashboard verification gate passes (499 tests plus typecheck, build, lint, governance, and packaged-asset checks)
• real-browser check confirmed 100 calls initially, 200 only after Load 100 more, and no console errors
• no local logs, private screenshots, or raw call content are committed