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/qr-generate.md

@@ -0,0 +1,71 @@
+---
+description: Generate QR codes with custom colors and error correction levels.
+---
+
+# QR Code Generator
+
+Generate QR code images from text or URLs with configurable size, error correction level, and custom foreground/background colors.
+
+## API Endpoint
+
+`POST /api/v1/tools/qr-generate`
+
+Accepts a **JSON body** (not multipart). No file upload is needed.
+
+## Parameters
+
+| Parameter | Type | Required | Default | Description |
+|-----------|------|----------|---------|-------------|
+| text | string | Yes | - | Content to encode in the QR code (1 to 2000 characters) |
+| size | number | No | `400` | Output image width/height in pixels (100 to 10000) |
+| errorCorrection | string | No | `"M"` | Error correction level: `L` (7%), `M` (15%), `Q` (25%), `H` (30%) |
+| foreground | string | No | `"#000000"` | QR code foreground/module color in hex (`#RRGGBB`) |
+| background | string | No | `"#FFFFFF"` | QR code background color in hex (`#RRGGBB`) |
+
+### Error Correction Levels
+
+| Level | Recovery | Use Case |
+|-------|----------|----------|
+| `L` | ~7% | Maximum data density |
+| `M` | ~15% | Balanced (default) |
+| `Q` | ~25% | Good for printed codes |
+| `H` | ~30% | Best for codes with logos overlay |
+
+## Example Request
+
+```bash
+curl -X POST http://localhost:1349/api/v1/tools/qr-generate \
+  -H "Authorization: Bearer si_your-api-key" \
+  -H "Content-Type: application/json" \
+  -d '{"text": "https://snapotter.com", "size": 500, "errorCorrection": "H"}'
+```
+
+Branded QR code with custom colors:
+
+```bash
+curl -X POST http://localhost:1349/api/v1/tools/qr-generate \
+  -H "Authorization: Bearer si_your-api-key" \
+  -H "Content-Type: application/json" \
+  -d '{"text": "Hello World", "size": 300, "foreground": "#1a365d", "background": "#f7fafc"}'
+```
+
+## Example Response
+
+```json
+{
+  "jobId": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
+  "downloadUrl": "/api/v1/download/a1b2c3d4-e5f6-7890-abcd-ef1234567890/qrcode.png",
+  "originalSize": 0,
+  "processedSize": 4520
+}
+```
+
+## Notes
+
+- This endpoint accepts JSON, not multipart form data, since no image upload is needed.
+- The output is always a PNG image.
+- The output filename is always `qrcode.png`.
+- `originalSize` is always 0 since this tool generates images from scratch.
+- A 2-module quiet zone (margin) is included around the QR code.
+- Maximum text length is 2000 characters. Actual capacity depends on error correction level and character encoding.
+- Higher error correction levels allow the QR code to remain scannable even if partially obscured but reduce data capacity.