refactor(ui): update menu, selector for TTY detection; thin dispatcher

- Update menu.ts and selector.ts to use isStdinTTY() and function-based
  terminal colors
- Refactor index.ts from 995-line monolith to ~270-line dispatcher that
  registers all commands via the CLI parser and delegates to modules
- Add initTTY() call at startup for correct pipe/TTY detection
- Interactive menu expanded to include new commands (explain, review,
  changelog, suggest, amend)

src/clipboard.ts

@@ -1,26 +1,26 @@
 export async function copyToClipboard(text: string): Promise<boolean> {
-  const commands: string[][] = [];
+    const commands: string[][] = [];
 
-  if (process.platform === "darwin") {
-    commands.push(["pbcopy"]);
-  } else if (process.platform === "linux") {
-    commands.push(["xclip", "-selection", "clipboard"]);
-    commands.push(["xsel", "--clipboard", "--input"]);
-  }
+    if (process.platform === "darwin") {
+        commands.push(["pbcopy"]);
+    } else if (process.platform === "linux") {
+        commands.push(["xclip", "-selection", "clipboard"]);
+        commands.push(["xsel", "--clipboard", "--input"]);
+    }
 
-  for (const cmd of commands) {
-    try {
-      const proc = Bun.spawn(cmd, {
-        stdin: "pipe",
-        stdout: "ignore",
-        stderr: "ignore",
-      });
-      proc.stdin.write(text);
-      proc.stdin.end();
-      const exitCode = await proc.exited;
-      if (exitCode === 0) return true;
-    } catch {}
-  }
+    for (const cmd of commands) {
+        try {
+            const proc = Bun.spawn(cmd, {
+                stdin: "pipe",
+                stdout: "ignore",
+                stderr: "ignore",
+            });
+            proc.stdin.write(text);
+            proc.stdin.end();
+            const exitCode = await proc.exited;
+            if (exitCode === 0) return true;
+        } catch {}
+    }
 
-  return false;
+    return false;
 }