feat: auto-generated per-repo webhook secrets with dashboard proxy

- Auto-generate webhook_secret on repository creation (UUID-based)
- Webhook routes use per-repo URLs: /webhook/{platform}/{repo_id}
- Verify signatures using per-repo secret (not global env var)
- Dashboard proxies webhooks to agent (agent not exposed publicly)
- Edit modal shows webhook URL + secret for user to copy into Gitea
- Add webhook-config API endpoint to retrieve per-repo secret
- Add Gitea option to edit dialog tracker type dropdown

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

compliance-dashboard/src/infrastructure/repositories.rs

@@ -216,6 +216,31 @@ pub async fn trigger_repo_scan(repo_id: String) -> Result<(), ServerFnError> {
     Ok(())
 }
 
+#[derive(Debug, Clone, Serialize, Deserialize, Default)]
+pub struct WebhookConfigResponse {
+    pub webhook_secret: Option<String>,
+    pub tracker_type: String,
+}
+
+#[server]
+pub async fn fetch_webhook_config(repo_id: String) -> Result<WebhookConfigResponse, ServerFnError> {
+    let state: super::server_state::ServerState =
+        dioxus_fullstack::FullstackContext::extract().await?;
+    let url = format!(
+        "{}/api/v1/repositories/{repo_id}/webhook-config",
+        state.agent_api_url
+    );
+
+    let resp = reqwest::get(&url)
+        .await
+        .map_err(|e| ServerFnError::new(e.to_string()))?;
+    let body: WebhookConfigResponse = resp
+        .json()
+        .await
+        .map_err(|e| ServerFnError::new(e.to_string()))?;
+    Ok(body)
+}
+
 /// Check if a repository has any running scans
 #[server]
 pub async fn check_repo_scanning(repo_id: String) -> Result<bool, ServerFnError> {