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/colorize.md

@@ -0,0 +1,73 @@
+# AI Colorization
+
+Convert black-and-white or grayscale photos to full color using AI (DDColor model with OpenCV DNN fallback).
+
+## API Endpoint
+
+`POST /api/v1/tools/colorize`
+
+**Processing:** Asynchronous (returns 202, poll `/api/v1/jobs/{jobId}/progress` for status via SSE)
+
+**Model bundle:** `object-eraser-colorize` (1-2 GB)
+
+## Parameters
+
+| Parameter | Type | Required | Default | Description |
+|-----------|------|----------|---------|-------------|
+| file | file | Yes | - | Image file (multipart) |
+| intensity | number | No | `1.0` | Color intensity (0-1). Lower values produce more subtle colorization |
+| model | string | No | `"auto"` | Model to use: `auto`, `ddcolor`, `opencv` |
+
+## Example Request
+
+```bash
+curl -X POST http://localhost:13490/api/v1/tools/colorize \
+  -F "file=@old-bw-photo.jpg" \
+  -F 'settings={"intensity":0.9,"model":"auto"}'
+```
+
+## Response
+
+### Initial Response (202 Accepted)
+
+```json
+{
+  "jobId": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
+  "async": true
+}
+```
+
+### Progress (SSE at `/api/v1/jobs/{jobId}/progress`)
+
+```
+event: progress
+data: {"phase":"processing","stage":"Colorizing...","percent":55}
+```
+
+### Final Result (via SSE)
+
+```json
+{
+  "phase": "complete",
+  "percent": 100,
+  "result": {
+    "jobId": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
+    "downloadUrl": "/api/v1/download/{jobId}/old-bw-photo_colorized.jpg",
+    "previewUrl": "/api/v1/download/{jobId}/preview.webp",
+    "originalSize": 180000,
+    "processedSize": 210000,
+    "width": 1920,
+    "height": 1080,
+    "method": "ddcolor"
+  }
+}
+```
+
+## Notes
+
+- Requires the `object-eraser-colorize` model bundle to be installed (1-2 GB).
+- DDColor produces higher quality results but is slower; OpenCV DNN is faster with slightly lower quality. `auto` uses DDColor when available with OpenCV fallback.
+- The `intensity` parameter blends between the original grayscale and the AI-colorized result. Use 1.0 for full color, lower values for a partially desaturated vintage look.
+- Output format matches the input format automatically.
+- For non-browser-previewable output formats, a WebP preview is generated alongside the main output.
+- Supports HEIC/HEIF, RAW, TGA, PSD, EXR, and HDR input formats via automatic decoding.