feat(#125): rename GITEA_URL to VCS_URL with deprecated fallback

- Add --vcs-url flag as primary (reads VCS_URL env var)
- Keep --gitea-url and GITEA_URL as deprecated fallbacks with warnings
- Update action.yml: rename gitea-url input to vcs-url, pass VCS_URL to binary
- Update ci.yml: use VCS_URL env var in Run review step
- Update integration tests: INTEGRATION_GITEA_URL -> INTEGRATION_VCS_URL
- Update README: --vcs-url / VCS_URL with fallback note in env var table

Backward compat: existing GITEA_URL users get a deprecation warning and
continue to work unchanged until they migrate to VCS_URL.

integration_test.go

@@ -16,16 +16,17 @@ import (
 
 // Integration test requires a running Gitea instance and LLM endpoint.
 // Set environment variables:
-//   INTEGRATION_GITEA_URL     - Gitea base URL
-//   INTEGRATION_GITEA_TOKEN   - Gitea API token with repo access
-//   INTEGRATION_GITEA_REPO    - owner/repo with an open PR
-//   INTEGRATION_PR_NUMBER     - PR number to test against
-//   INTEGRATION_LLM_BASE_URL  - LLM API base URL
-//   INTEGRATION_LLM_API_KEY   - LLM API key
-//   INTEGRATION_LLM_MODEL     - Model name
+//
+//	INTEGRATION_VCS_URL       - VCS base URL
+//	INTEGRATION_GITEA_TOKEN   - Gitea API token with repo access
+//	INTEGRATION_GITEA_REPO    - owner/repo with an open PR
+//	INTEGRATION_PR_NUMBER     - PR number to test against
+//	INTEGRATION_LLM_BASE_URL  - LLM API base URL
+//	INTEGRATION_LLM_API_KEY   - LLM API key
+//	INTEGRATION_LLM_MODEL     - Model name
 
 func TestIntegration_FullReviewFlow(t *testing.T) {
-	giteaURL := os.Getenv("INTEGRATION_GITEA_URL")
+	giteaURL := os.Getenv("INTEGRATION_VCS_URL")
 	giteaToken := os.Getenv("INTEGRATION_GITEA_TOKEN")
 	giteaRepo := os.Getenv("INTEGRATION_GITEA_REPO")
 	prNumStr := os.Getenv("INTEGRATION_PR_NUMBER")