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/api/ai.md

@@ -6,7 +6,7 @@ description: AI engine reference with all local ML tools. Background removal, up
 
 The `@snapotter/ai` package bridges Node.js to a **persistent Python sidecar** for all ML operations. The dispatcher process stays alive between requests for fast warm-start performance. GPU is auto-detected at startup and used when available.
 
-19 Python sidecar AI tools across four modalities (image, audio, video, document), plus 2 tools with optional AI capabilities. All models run locally -- no internet required after initial model download.
+19 Python sidecar AI tools across four modalities (image, audio, video, document), plus 2 tools with optional AI capabilities. All models run locally - no internet required after initial model download.
 
 ## Architecture
 
@@ -406,7 +406,7 @@ An additional analysis endpoint is available at `POST /api/v1/tools/image/image-
 ### Content-Aware Resize (Seam Carving)
 
 **Tool route:** `content-aware-resize`  
-**Engine:** Go `caire` binary (not Python -- no GPU benefit)
+**Engine:** Go `caire` binary (not Python - no GPU benefit)
 
 Intelligently resizes images by removing low-energy seams, preserving important content.