docs: comprehensive documentation overhaul

Add complete documentation structure:
- Frontend architecture documentation
- Database schema documentation
- Deployment guides (Docker, Traefik, Authentik, Environment)
- Development guides (Setup, Testing, Contributing, Quality Gates)
- Deployment architecture documentation
- Updated docs README with complete navigation

All new features and APIs are now documented.
Quality gates: docs only, no code changes

docs/templates/api-endpoint.md

@@ -0,0 +1,97 @@
+# API Endpoint Documentation Template
+
+Use this template when documenting API endpoints.
+
+## Endpoint Group Name
+
+Brief description of what this group of endpoints does.
+
+### Authentication
+
+Describe authentication requirements (e.g., "Requires valid session cookie").
+
+---
+
+## METHOD /path/to/endpoint
+
+**Description:** What this endpoint does.
+
+### Request
+
+#### Headers
+
+| Header | Required | Description |
+|--------|----------|-------------|
+| `Authorization` | Yes/No | Description |
+| `Content-Type` | Yes/No | Description |
+
+#### Query Parameters
+
+| Parameter | Type | Required | Description |
+|-----------|------|----------|-------------|
+| `param_name` | `string` | Yes/No | Description |
+
+#### Request Body
+
+```json
+{
+  "field_name": "string",
+  "field_name": "number"
+}
+```
+
+| Field | Type | Required | Description |
+|-------|------|----------|-------------|
+| `field_name` | `string` | Yes/No | Description |
+
+### Response
+
+#### Success (200 OK)
+
+```json
+{
+  "field_name": "value",
+  "field_name": "value"
+}
+```
+
+#### Error Responses
+
+**400 Bad Request**
+```json
+{
+  "detail": "Error message"
+}
+```
+
+**401 Unauthorized**
+```json
+{
+  "detail": "Authentication required"
+}
+```
+
+### Example
+
+#### Request
+```bash
+curl -X METHOD http://api.example.com/path/to/endpoint \
+  -H "Content-Type: application/json" \
+  -H "Cookie: session=your_session_cookie" \
+  -d '{
+    "field_name": "value"
+  }'
+```
+
+#### Response
+```json
+{
+  "field_name": "value"
+}
+```
+
+---
+
+## METHOD /path/to/another/endpoint
+
+[Repeat the same structure for each endpoint]