feat(integrations): add review fetching and Linux keyring support

Add a cross-provider Review Center and improve credential handling.
Backend integrations fetch and normalize PRs from GitHub, GitLab,
Gitea, and Azure DevOps with improved timeouts and parsing. Credentials
now use a global lock and support secret-tool on Linux to avoid races.

- Normalize review data across providers (GitHub/GitLab/Gitea/Azure)
- Serialize credential access with OnceLock and use secret-tool on Linux
- Add frontend ReviewCenter component and related UI updates

src/lib/types.ts

@@ -65,6 +65,39 @@ export interface GitIntegrationRepository {
   private: boolean;
 }
 
+export type IntegrationReviewState = "open" | "draft" | "merged" | "closed";
+export type IntegrationReviewAction = "merge" | "approve" | "close" | "reopen";
+
+export interface IntegrationReviewComment {
+  id: string;
+  author: string;
+  body: string;
+  createdAt: string;
+}
+
+export interface IntegrationReviewRequest {
+  id: string;
+  number: number;
+  provider: GitIntegrationProvider;
+  repositoryId: string;
+  repositoryName: string;
+  title: string;
+  description: string;
+  author: string;
+  state: IntegrationReviewState;
+  sourceBranch: string;
+  targetBranch: string;
+  webUrl: string;
+  createdAt: string;
+  updatedAt: string;
+  collaborators: string[];
+  additions: number | null;
+  deletions: number | null;
+  changedFiles: number | null;
+  mergeStatus: "" | "mergeable" | "conflicts" | "checking" | "blocked";
+  comments: IntegrationReviewComment[];
+}
+
 export interface CustomThemeColors {
   background: string;
   surface: string;