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/audio/audio-speed.md

@@ -0,0 +1,45 @@
+---
+description: Speed up or slow down audio playback with a multiplier.
+---
+
+# Audio Speed
+
+Speed up or slow down audio playback by applying a speed multiplier.
+
+## API Endpoint
+
+`POST /api/v1/tools/audio/audio-speed`
+
+Accepts multipart form data with an audio file and a JSON `settings` field.
+
+## Parameters
+
+| Parameter | Type | Required | Default | Description |
+|-----------|------|----------|---------|-------------|
+| factor | number | No | `1.5` | Speed multiplier (0.25 to 4). Values below 1 slow down; above 1 speed up. |
+
+## Example Request
+
+```bash
+curl -X POST http://localhost:1349/api/v1/tools/audio/audio-speed \
+  -H "Authorization: Bearer si_your-api-key" \
+  -F "file=@audio.mp3" \
+  -F 'settings={"factor": 2}'
+```
+
+## Example Response
+
+```json
+{
+  "jobId": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
+  "downloadUrl": "/api/v1/download/a1b2c3d4-e5f6-7890-abcd-ef1234567890/audio.mp3",
+  "originalSize": 4500000,
+  "processedSize": 2250000
+}
+```
+
+## Notes
+
+- A factor of `0.25` plays at quarter speed (4x longer). A factor of `4` plays at quadruple speed (4x shorter).
+- Pitch changes proportionally with speed. Use pitch-shift if you need to adjust pitch independently.
+- Output format matches the input format.