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/api/users.md

@@ -0,0 +1,168 @@
+# Users API
+
+User profile and settings management.
+
+## Authentication
+
+All endpoints require authentication (session cookie).
+
+---
+
+## GET /users/me
+
+**Description:** Get current user profile.
+
+### Response
+
+#### Success (200 OK)
+
+```json
+{
+  "id": "uuid",
+  "email": "user@example.com",
+  "name": "User Name",
+  "avatar_url": "https://...",
+  "authentik_id": "authentik-uuid",
+  "created_at": "2024-01-01T00:00:00Z",
+  "updated_at": "2024-01-01T00:00:00Z"
+}
+```
+
+---
+
+## PUT /users/me
+
+**Description:** Update user profile.
+
+### Request
+
+#### Request Body
+
+```json
+{
+  "name": "New Name",
+  "email": "newemail@example.com"
+}
+```
+
+| Field | Type | Required | Description |
+|-------|------|----------|-------------|
+| `name` | `string` | No | New display name |
+| `email` | `string` | No | New email address |
+
+### Response
+
+#### Success (200 OK)
+
+```json
+{
+  "id": "uuid",
+  "email": "newemail@example.com",
+  "name": "New Name",
+  "avatar_url": "https://...",
+  "updated_at": "2024-01-02T00:00:00Z"
+}
+```
+
+---
+
+## POST /users/me/avatar
+
+**Description:** Upload avatar image.
+
+### Request
+
+#### Request Body
+
+Multipart form data with `file` field.
+
+**Requirements:**
+- Format: PNG or JPEG
+- Max size: 2MB
+
+### Response
+
+#### Success (200 OK)
+
+```json
+{
+  "avatar_url": "/uploads/avatars/uuid.png"
+}
+```
+
+#### Error (400 Bad Request)
+
+```json
+{
+  "detail": "Invalid file format. Only PNG and JPEG are allowed."
+}
+```
+
+---
+
+## GET /users/me/config
+
+**Description:** Get user settings.
+
+### Response
+
+#### Success (200 OK)
+
+```json
+{
+  "id": "uuid",
+  "user_id": "uuid",
+  "config": {
+    "theme": "dark",
+    "git_identity": {
+      "name": "User Name",
+      "email": "user@example.com"
+    },
+    "default_editor": "code-server"
+  }
+}
+```
+
+---
+
+## PATCH /users/me/config
+
+**Description:** Update user settings.
+
+### Request
+
+#### Request Body
+
+```json
+{
+  "theme": "light",
+  "git_identity": {
+    "name": "New Name",
+    "email": "new@example.com"
+  }
+}
+```
+
+| Field | Type | Required | Description |
+|-------|------|----------|-------------|
+| `theme` | `string` | No | "system", "light", or "dark" |
+| `git_identity` | `object` | No | `{name, email}` |
+| `default_editor` | `string` | No | Preferred editor |
+
+### Response
+
+#### Success (200 OK)
+
+```json
+{
+  "id": "uuid",
+  "user_id": "uuid",
+  "config": {
+    "theme": "light",
+    "git_identity": {
+      "name": "New Name",
+      "email": "new@example.com"
+    }
+  }
+}
+```