feat(mockups): four search-header redesign directions

[BigSimmo]

Summary

• Adds /mockups/search-header-redesign with four redesign concepts for the shared search-results header chrome used across search pages.
• Each concept shows desktop and phone in the same frame, targeting the current stacked-pill layout (mode pill, redundant Search chip, bordered query card, Relevance/A–Z pills, Results/Forms tabs).
• Directions:
  1. Ledger strip — typography-first strip; no nested card; underline sort
  2. Command mast — dense instrument bar; quiet mode label; one control height
  3. Unified chrome — mode + query + count share one header owner; Search chip removed
  4. Focus frame — single accent edge; phone refine disclosure; calm desktop utilities
• Suppresses shared mockup shell chrome so framed concepts are the only header on the page.
• Updates docs/site-map.md and adds mockups/search-header-redesign.md notes.

Preview

Ledger strip desktop and phone
Command mast desktop and phone
Unified chrome desktop and phone
Focus frame desktop and phone

Test plan

• Open /mockups/search-header-redesign in development
• Confirm all four sections render desktop + phone side by side
• Interact with sort segments, category tabs, and Focus refine disclosure on phone
• Confirm shared mockup header/composer are hidden on this route

Clinical Governance Preflight

• Not applicable — design-scratch mockups only; no clinical, retrieval, ingestion, privacy, or production-env changes.

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[supabase]

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[BigSimmo]

Temporarily closing to preserve the serialized merge queue while #1485 exact-head CI runs. This PR will be reviewed in a later queue slot.