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/ssh-keys.md

@@ -0,0 +1,77 @@
+# SSH Keys API
+
+SSH key management endpoints.
+
+## Authentication
+
+All endpoints require authentication (session cookie).
+
+---
+
+## GET /ssh-keys
+
+**Description:** List all SSH keys for the current user.
+
+### Response
+
+#### Success (200 OK)
+
+```json
+[
+  {
+    "id": "uuid",
+    "name": "GitHub Work",
+    "public_key": "ssh-ed25519 AAAAC3NzaC... user@example.com",
+    "created_at": "2024-01-01T00:00:00Z"
+  }
+]
+```
+
+**Note:** Private keys are never returned.
+
+---
+
+## POST /ssh-keys
+
+**Description:** Generate a new SSH key pair.
+
+### Request
+
+#### Request Body
+
+```json
+{
+  "name": "GitHub Personal"
+}
+```
+
+| Field | Type | Required | Description |
+|-------|------|----------|-------------|
+| `name` | `string` | Yes | Key name/label |
+
+### Response
+
+#### Success (201 Created)
+
+```json
+{
+  "id": "uuid",
+  "name": "GitHub Personal",
+  "public_key": "ssh-ed25519 AAAAC3NzaC... user@example.com",
+  "created_at": "2024-01-01T00:00:00Z"
+}
+```
+
+**Note:** The private key is generated and stored securely. It is not returned in the response.
+
+---
+
+## DELETE /ssh-keys/{id}
+
+**Description:** Delete an SSH key.
+
+### Response
+
+#### Success (204 No Content)
+
+**Note:** This permanently deletes both public and private keys.