Adds an always-visible debounced search input in the AppShell header
that fans out to three independent sources in parallel and renders
per-source result groups with their own loading/empty/error states:
- /api/search/cases (NEW): SQL ILIKE on case_number, address, parties,
title, subject. Returns small projections, no embeddings needed.
- /api/precedent-library/search (existing): semantic over case-law
halachot + passages.
- /api/search (existing): semantic over case documents + past decisions.
Cmd/Ctrl+K focuses the input; Esc and click-outside close the panel.
This is Phase A of the header redesign — the bar layout itself is
unchanged; row grouping + dynamic context follow in Phase B.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
