Improve docs search UX, dash cleanup, and colored modality tool icons (#338)

* feat(docs): improve search UX

- Hide the 'Search by Pagefind' branding in the search dialog footer
- Replace the 'No results found.' message shown before any query with a
  friendly hint (detected via empty-input :placeholder-shown state)
- Tune placeholder, empty-state, and results-heading copy; show a few
  sub-section matches per result (pageResultCount)

* docs: replace double-dash em-dash substitute with single dash

Swept prose ' -- ' to ' - ' and numeric ranges (e.g. 2--20 to 2-20)
across the documentation. CLI flags and code blocks left untouched.

* fix(landing): show colored category icons on modality tool pages

The /tools/<modality>/ pages rendered bare name+description cards with no
icon or color. Port the colored, category-tinted icon card from /tools/
so modality pages match the main catalog (icon, tint, 'Learn more').

apps/docs/guide/developer.md

@@ -79,7 +79,7 @@ pnpm test:coverage      # tests with coverage report
 
 ## Database
 
-PostgreSQL 17 via Drizzle ORM (pg-core). Local dev requires Postgres and Redis running -- start them with:
+PostgreSQL 17 via Drizzle ORM (pg-core). Local dev requires Postgres and Redis running - start them with:
 
 ```bash
 docker compose -f docker-compose.dev.yml up -d