docs: organize tool pages by modality under /tools/<modality>/

Move all 157 tool pages into image/video/audio/pdf/data subfolders so URLs read /tools/<modality>/<id> (e.g. /tools/image/crop). Nest the image sub-categories under an Image group in the sidebar so the nav reads by modality. Add public/_redirects (301, clean + .html forms) mapping every old flat /tools/<id> URL to its new path so inbound links keep working. Rewrite all internal /tools links. Verified with a clean docs build (no dead links).

apps/docs/tools/video/video-to-frames.md

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+---
+description: Extract frames from a video as a ZIP of images.
+---
+
+# Video to Frames
+
+Extract individual frames from a video and download them as a ZIP archive of PNG or JPG images.
+
+## API Endpoint
+
+`POST /api/v1/tools/video/video-to-frames`
+
+Accepts multipart form data with a video file and a JSON `settings` field.
+
+## Parameters
+
+| Parameter | Type | Required | Default | Description |
+|-----------|------|----------|---------|-------------|
+| mode | string | No | `"all"` | Extraction mode: `all`, `nth`, `timestamps` |
+| n | integer | No | `10` | Extract every Nth frame (2-1000). Only used when mode is `"nth"` |
+| timestamps | string | No | `""` | Comma-separated timestamps in seconds. Required when mode is `"timestamps"` |
+| format | string | No | `"png"` | Image format for extracted frames: `png`, `jpg` |
+
+## Example Request
+
+Extract every 30th frame as JPG:
+
+```bash
+curl -X POST http://localhost:1349/api/v1/tools/video/video-to-frames \
+  -H "Authorization: Bearer si_your-api-key" \
+  -F "file=@clip.mp4" \
+  -F 'settings={"mode": "nth", "n": 30, "format": "jpg"}'
+```
+
+Extract frames at specific timestamps:
+
+```bash
+curl -X POST http://localhost:1349/api/v1/tools/video/video-to-frames \
+  -H "Authorization: Bearer si_your-api-key" \
+  -F "file=@clip.mp4" \
+  -F 'settings={"mode": "timestamps", "timestamps": "1.5,5,12.3"}'
+```
+
+## Example Response
+
+```json
+{
+  "jobId": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
+  "downloadUrl": "/api/v1/download/a1b2c3d4-e5f6-7890-abcd-ef1234567890/clip-frames.zip",
+  "originalSize": 12500000,
+  "processedSize": 45000000
+}
+```
+
+## Notes
+
+- The `all` mode extracts every frame and can produce very large ZIP files for long videos. Use `nth` or `timestamps` mode for selective extraction.
+- PNG preserves full quality but produces larger files. JPG is smaller but lossy.
+- The response downloads as a ZIP archive containing sequentially numbered image files.