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/tools/files/split-csv.md

@@ -16,7 +16,7 @@ Accepts multipart form data with a CSV file and a JSON `settings` field.
 
 | Parameter | Type | Required | Default | Description |
 |-----------|------|----------|---------|-------------|
-| rowsPerFile | integer | No | `1000` | Number of data rows per output file (1--1,000,000) |
+| rowsPerFile | integer | No | `1000` | Number of data rows per output file (1-1,000,000) |
 | keepHeader | boolean | No | `true` | Repeat the header row in each output file |
 
 ## Example Request