feat: implement API versioning /api/v1/

- All backend routers moved to /api/v1/ prefix
- Frontend BASE_URL updated to /api/v1
- Setup redirect middleware updated to redirect to /api/v1/setup
- Health router path fixed: prefix=/api/v1/health, @router.get('')
- conftest.py: set server_status=online for test fixture
- Created Docs/API_VERSIONING.md with deprecation policy
- Updated Docs/Backend-Development.md with versioning section
- Updated Instructions.md curl examples

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

backend/app/config.py

@@ -380,6 +380,22 @@ class Settings(BaseSettings):
             "Larger batches are more efficient but introduce slight latency."
         ),
     )
+    # Rate limit configuration (per IP)
+    rate_limit_bans_per_minute: int = Field(
+        default=100,
+        ge=1,
+        description="Max ban/unban requests per IP per minute.",
+    )
+    rate_limit_blocklist_import_per_hour: int = Field(
+        default=10,
+        ge=1,
+        description="Max blocklist import requests per IP per hour.",
+    )
+    rate_limit_config_update_per_minute: int = Field(
+        default=50,
+        ge=1,
+        description="Max config update requests per IP per minute.",
+    )
 
     @field_validator("elasticsearch_hosts", mode="before")
     @classmethod