Multi-category search router for the observatory home.

The welcome-observatory.html search input promises "search — AAPL, personal finance, today's headlines." This route honours that promise: it routes a user's query to the most relevant surface based on shape:

1. Empty query → back to /welcome
2. Known keyword (case-insensitive) → mapped surface
3. Symbol shape (≤6 chars, alphanumeric + dot/dash) → resolved against the company catalog (S1, 2026-09-25): a known ticker redirects as itself, a company NAME ("Apple") redirects to its ticker (AAPL), and an unknown string carries a lookup= hint so the client shows "no company called X" rather than the financial-statements copy
4. Concept shape (whitespace / punctuation / long) → /?view=learn
5. Else → the same catalog resolution, then the ticker fallback

Phase 1H will replace this with full autocomplete + a proper search-results page; this version handles the common shapes.