Add read-only repository viewer (UI + backend)

Implements a read-only repository viewer for remote Gitea repos and local clones. Adds UI/CSS for viewer panels, breadcrumb/branch controls, file table, code/Markdown preview, and readme rendering (frontend/css/components.css, frontend/js/app.js). Extends app state and wiring (state.js, app.js) with viewer actions, branch/content loading, local/remote navigation, and preview helpers (base64 decoding, markdown rendering, syntax highlighting, 256 KB preview limit). Adds Gitea API helpers to fetch repo branches and contents (frontend/js/gitea-api.js) and Tauri JS bindings for local repo operations (tauri-api.js). Implements Rust backend commands to list branches, tree entries, and file contents (with size/binary checks and helper utilities) and wires them into the Tauri command registry (src-tauri/src/lib.rs). Also updates README to mention the new read-only viewer.

frontend/js/tauri-api.js

@@ -35,6 +35,31 @@ export async function runGitBranch(repoPath, gitPath) {
   return invoke("git_branch", { repoPath, gitPath: gitPath || null });
 }
 
+export async function listLocalRepoBranches(repoPath, gitPath) {
+  ensureInvoke();
+  return invoke("local_repo_branches", { repoPath, gitPath: gitPath || null });
+}
+
+export async function listLocalRepoTree(repoPath, reference, path, gitPath) {
+  ensureInvoke();
+  return invoke("local_repo_tree", {
+    repoPath,
+    reference,
+    path: path || "",
+    gitPath: gitPath || null,
+  });
+}
+
+export async function readLocalRepoFile(repoPath, reference, path, gitPath) {
+  ensureInvoke();
+  return invoke("local_repo_file", {
+    repoPath,
+    reference,
+    path,
+    gitPath: gitPath || null,
+  });
+}
+
 export async function testGiteaConnection(payload) {
   ensureInvoke();
   return invoke("test_gitea_connection", payload);