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/data/yaml-json.md

@@ -0,0 +1,52 @@
+---
+description: Convert between YAML and JSON, both directions.
+---
+
+# YAML / JSON
+
+Convert between YAML and JSON formats in both directions. Upload a YAML file to get JSON, or upload a JSON file to get YAML.
+
+## API Endpoint
+
+`POST /api/v1/tools/data/yaml-json`
+
+Accepts multipart form data with a YAML or JSON file. No settings field is required.
+
+## Parameters
+
+This tool has no configurable parameters. The conversion direction is determined by the input file extension.
+
+## Example Request
+
+YAML to JSON:
+
+```bash
+curl -X POST http://localhost:1349/api/v1/tools/data/yaml-json \
+  -H "Authorization: Bearer si_your-api-key" \
+  -F "file=@config.yaml"
+```
+
+JSON to YAML:
+
+```bash
+curl -X POST http://localhost:1349/api/v1/tools/data/yaml-json \
+  -H "Authorization: Bearer si_your-api-key" \
+  -F "file=@config.json"
+```
+
+## Example Response
+
+```json
+{
+  "jobId": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
+  "downloadUrl": "/api/v1/download/a1b2c3d4-e5f6-7890-abcd-ef1234567890/config.json",
+  "originalSize": 620,
+  "processedSize": 780
+}
+```
+
+## Notes
+
+- Conversion direction is auto-detected from the input file extension: `.yaml` or `.yml` produces `.json`, and `.json` produces `.yaml`.
+- Both `.yaml` and `.yml` extensions are accepted.
+- Multi-document YAML files (separated by `---`) are supported.