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/transcribe-audio.md

@@ -0,0 +1,50 @@
+---
+description: Convert speech to text with AI-powered transcription.
+---
+
+# Transcribe Audio
+
+Convert speech to text using AI-powered transcription (faster-whisper). Supports plain text, SRT, and VTT output formats with automatic or manual language selection.
+
+## API Endpoint
+
+`POST /api/v1/tools/audio/transcribe-audio`
+
+Accepts multipart form data with an audio file and a JSON `settings` field.
+
+## Parameters
+
+| Parameter | Type | Required | Default | Description |
+|-----------|------|----------|---------|-------------|
+| language | string | No | `"auto"` | Language: `auto`, `en`, `de`, `fr`, `es`, `zh`, `ja`, `ko`, `id`, `th`, `vi` |
+| outputFormat | string | No | `"txt"` | Output format: `txt`, `srt`, `vtt` |
+
+## Example Request
+
+```bash
+curl -X POST http://localhost:1349/api/v1/tools/audio/transcribe-audio \
+  -H "Authorization: Bearer si_your-api-key" \
+  -F "file=@audio.mp3" \
+  -F 'settings={"language": "en", "outputFormat": "srt"}'
+```
+
+## Example Response
+
+This is an async tool. The API returns `202 Accepted` immediately:
+
+```json
+{
+  "jobId": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
+  "async": true
+}
+```
+
+Track progress via SSE at `GET /api/v1/jobs/{jobId}/progress`. When the job completes, the SSE stream delivers the final result with a `downloadUrl`.
+
+## Notes
+
+- Requires the **transcription** feature bundle to be installed. Returns `501 Not Implemented` if the bundle is not available.
+- Uses faster-whisper for transcription. Language `auto` detects the spoken language automatically.
+- `srt` and `vtt` formats include timestamps for each segment, suitable for subtitles.
+- `txt` format returns plain text without timestamps.
+- This is a long-running AI tool; processing time depends on audio length and server hardware.