Complete implementation planning for CLI app with MFA

- Created implementation plan with technical context
- Developed data models for User Session, Sync Job, and Authentication Token
- Defined API contracts for authentication, sync triggering, and status checking
- Created quickstart guide for CLI usage
- Updated agent context with new technology stack
- Verified constitution compliance for all design decisions

specs/006-cli-auth-sync-mfa/contracts/auth_cli_login.yaml

@@ -0,0 +1,112 @@
+openapi: 3.0.0
+info:
+  title: GarminSync CLI Authentication API
+  version: 1.0.0
+  description: API for CLI-based authentication with MFA support
+paths:
+  /api/auth/cli/login:
+    post:
+      summary: Authenticate user via CLI with optional MFA
+      description: Authenticates a user with username/password and optional MFA code
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              type: object
+              required:
+                - username
+                - password
+              properties:
+                username:
+                  type: string
+                  description: User's email or username
+                password:
+                  type: string
+                  description: User's password
+                mfa_code:
+                  type: string
+                  description: MFA code if required
+                remember_me:
+                  type: boolean
+                  description: Whether to store tokens for future use
+      responses:
+        '200':
+          description: Authentication successful
+          content:
+            application/json:
+              schema:
+                type: object
+                properties:
+                  success:
+                    type: boolean
+                    example: true
+                  session_id:
+                    type: string
+                    description: Unique session identifier
+                  access_token:
+                    type: string
+                    description: Access token for API calls
+                  token_type:
+                    type: string
+                    description: Type of token (e.g., Bearer)
+                  expires_in:
+                    type: integer
+                    description: Time until token expiration in seconds
+                  mfa_required:
+                    type: boolean
+                    description: Whether MFA is required for this account
+                  user:
+                    type: object
+                    properties:
+                      id:
+                        type: string
+                        description: User identifier
+                      email:
+                        type: string
+                        description: User's email
+                      username:
+                        type: string
+                        description: User's username
+        '400':
+          description: Invalid credentials or missing required fields
+          content:
+            application/json:
+              schema:
+                type: object
+                properties:
+                  success:
+                    type: boolean
+                    example: false
+                  error:
+                    type: string
+                    description: Error message
+                  mfa_required:
+                    type: boolean
+                    description: Whether MFA is required for this account
+        '401':
+          description: Authentication failed
+          content:
+            application/json:
+              schema:
+                type: object
+                properties:
+                  success:
+                    type: boolean
+                    example: false
+                  error:
+                    type: string
+                    description: Error message
+        '429':
+          description: Too many failed attempts
+          content:
+            application/json:
+              schema:
+                type: object
+                properties:
+                  success:
+                    type: boolean
+                    example: false
+                  error:
+                    type: string
+                    description: Error message