docs: add per-tool API documentation and fix parity gaps

- Create 53 per-tool VitePress documentation pages with accurate
  parameters from Zod schemas, example requests, and response formats
- Add root llms.txt for LLM-friendly repo browsing
- Fix OpenAPI spec: add auth and 422 error schemas to
  edit-metadata/inspect and strip-metadata/inspect sub-routes
- Fix tool count inconsistency (52 -> 53) across landing site,
  e2e tests, and local docs
- Rename color-adjustments.ts to adjust-colors.ts to match tool ID
- Update VitePress sidebar with all 8 tool categories and top nav

apps/docs/tools/text-overlay.md

@@ -0,0 +1,63 @@
+---
+description: Add styled text overlays with drop shadows and background boxes.
+---
+
+# Text Overlay
+
+Add styled text to images with optional drop shadow and semi-transparent background box. Suitable for titles, captions, or annotations on photos.
+
+## API Endpoint
+
+`POST /api/v1/tools/text-overlay`
+
+Accepts multipart form data with an image file and a JSON `settings` field.
+
+## Parameters
+
+| Parameter | Type | Required | Default | Description |
+|-----------|------|----------|---------|-------------|
+| text | string | Yes | - | Text to overlay (1 to 500 characters) |
+| fontSize | number | No | `48` | Font size in pixels (8 to 200) |
+| color | string | No | `"#FFFFFF"` | Text color in hex format (`#RRGGBB`) |
+| position | string | No | `"bottom"` | Vertical placement: `top`, `center`, `bottom` |
+| backgroundBox | boolean | No | `false` | Show a semi-transparent background rectangle behind the text |
+| backgroundColor | string | No | `"#000000"` | Background box color in hex format (`#RRGGBB`) |
+| shadow | boolean | No | `true` | Apply a drop shadow behind the text |
+
+## Example Request
+
+```bash
+curl -X POST http://localhost:1349/api/v1/tools/text-overlay \
+  -H "Authorization: Bearer si_your-api-key" \
+  -F "file=@photo.jpg" \
+  -F 'settings={"text": "Hello World", "fontSize": 64, "color": "#FFFFFF", "position": "bottom", "shadow": true}'
+```
+
+With a background box:
+
+```bash
+curl -X POST http://localhost:1349/api/v1/tools/text-overlay \
+  -H "Authorization: Bearer si_your-api-key" \
+  -F "file=@photo.jpg" \
+  -F 'settings={"text": "Caption", "fontSize": 36, "position": "bottom", "backgroundBox": true, "backgroundColor": "#000000"}'
+```
+
+## Example Response
+
+```json
+{
+  "jobId": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
+  "downloadUrl": "/api/v1/download/a1b2c3d4-e5f6-7890-abcd-ef1234567890/photo.jpg",
+  "originalSize": 2450000,
+  "processedSize": 2470000
+}
+```
+
+## Notes
+
+- Text is always centered horizontally within the image.
+- The drop shadow uses a 2px offset with 3px blur at 70% black opacity.
+- The background box spans the full image width at 70% opacity, with height proportional to the font size (1.8x).
+- Text is rendered via SVG composite, so the system's default sans-serif font is used.
+- XML-special characters in the text are safely escaped.
+- Output format matches the input format. HEIC, RAW, PSD, and SVG inputs are automatically decoded before processing.