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/.vitepress/config.mts

@@ -49,7 +49,14 @@ export default defineConfig({
 
   vite: {
     plugins: [
-      pagefindPlugin(),
+      pagefindPlugin({
+        btnPlaceholder: "Search",
+        placeholder: "Search tools, guides, and the API…",
+        emptyText: "No matches found. Try a different term or check the spelling.",
+        heading: "{{searchResult}} results",
+        // Show a few sub-section matches per page so deep-linked headings surface.
+        pageResultCount: 3,
+      }),
       llmstxt({
         domain: "https://docs.snapotter.com",
         customLLMsTxtTemplate: `# {title}