Fix Terraform skill frictions (#103)

Fix Terraform skill to use latest Google provider version
Add constraint to force using Developer Connect when creating Cloud Build trigger
Fix Terraform skill to use Developer Connect instead of Firebase as GitHub app for DC connection

Author: CoasterJX

skills/gcp-cicd-terraform/SKILL.md

@@ -30,6 +30,27 @@ terraform {
 
 Note: The GCS bucket must have Object Versioning enabled to allow recovery from accidental state corruption or overlapping writes.
 
+### Required Provider Version
+Use the Google Cloud Terraform provider version 7.20.0 or higher. This skill utilizes features (e.g., Developer Connect) introduced in Google Provider v7.20.0.
+
+```hcl
+terraform {
+  required_version = ">= 1.6.0"
+
+  required_providers {
+    google = {
+      source  = "hashicorp/google"
+      version = ">= 7.20.0" 
+    }
+  }
+}
+```
+
+To retrieve the latest version of the Google provider, use the following command:
+```bash
+curl -s https://registry.terraform.io/v1/providers/hashicorp/google | jq -r .version
+```
+
 ## 🛠️ Execution Protocol (Safety First)
 The Agent must follow this lifecycle for every infrastructure change to ensure idempotency and prevent production outages:
 
@@ -88,6 +109,44 @@ To maintain a clean module interface, use the main identifier for singleton reso
    - Private Google Access: Subnets should always have private_ip_google_access = true.
    - Workload Identity: Prefer GKE Workload Identity over static Service Account JSON keys.
 
+3. Cloud Build Triggers with Developer Connect
+   When using Developer Connect git repository links, use `developer_connect_event_config` — NOT `repository_event_config`. The `repository_event_config` block is for Cloud Build v2 repository connections and will not work with Developer Connect resources. An example block to create a Cloud Build trigger with Developer Connect git repository link is as follows:
+
+    ```hcl
+    resource "google_cloudbuild_trigger" "main" {
+      developer_connect_event_config {
+        git_repository_link = google_developer_connect_git_repository_link.main.id
+        push {
+          branch = var.trigger_branch
+        }
+      }
+    }
+    ```
+
+4. Developer Connect Connection
+   When configuring `google_developer_connect_connection`, always set `github_app` to `"DEVELOPER_CONNECT"`. Using `"FIREBASE"` is incorrect and will cause triggers to fail.
+
+    ```hcl
+    resource "google_developer_connect_connection" "main" {
+      location      = var.region
+      connection_id = var.connection_id
+      project       = var.project_id
+
+      github_config {
+        github_app = "DEVELOPER_CONNECT" # CORRECT
+        authorizer_credential {
+          oauth_token_secret_version = "" # Populated after manual authorization
+        }
+      }
+
+      depends_on = [google_project_service.main["developerconnect.googleapis.com"]]
+
+      lifecycle {
+        ignore_changes = [github_config[0].authorizer_credential]
+      }
+    }
+    ```
+
 ## 📂 Directory Structure
 Follow this standard to ensure compatibility with Antigravity (AGY) discovery and Google best practices: