batch3 T4: file_ops + file_index services; UI endpoints; tools refactor

- services/file_ops.ts: shared listDir/viewFile/grep/findFiles core
- services/file_index.ts: per-project flat file list cached on mtime of
  project root + .git/HEAD + .git/index (rg --files honors .gitignore)
- services/tools.ts: tools delegate to file_ops, output format unchanged
- routes/projects.ts: GET /list_dir, /view_file, /files endpoints
- web client: api.projects.listDir/viewFile/files + mirrored types

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/server/src/services/file_index.ts

@@ -0,0 +1,49 @@
+import fs from 'node:fs/promises';
+import path from 'node:path';
+import { execFile } from 'node:child_process';
+
+interface MtimeSnap {
+  root: number;
+  gitHead: number | null;
+  gitIndex: number | null;
+}
+
+interface CacheEntry {
+  files: string[];
+  mtimes: MtimeSnap;
+}
+
+const cache = new Map<string, CacheEntry>(); // keyed by projectId
+
+export async function getProjectFiles(projectId: string, projectRoot: string): Promise<string[]> {
+  const current = await snapMtimes(projectRoot);
+  const cached = cache.get(projectId);
+  if (cached && eqMtimes(cached.mtimes, current)) {
+    return cached.files;
+  }
+  const files = await runRgFiles(projectRoot);
+  cache.set(projectId, { files, mtimes: current });
+  return files;
+}
+
+async function snapMtimes(root: string): Promise<MtimeSnap> {
+  const rootStat = await fs.stat(root);
+  let gitHead: number | null = null;
+  let gitIndex: number | null = null;
+  try { gitHead = (await fs.stat(path.join(root, '.git', 'HEAD'))).mtimeMs; } catch {}
+  try { gitIndex = (await fs.stat(path.join(root, '.git', 'index'))).mtimeMs; } catch {}
+  return { root: rootStat.mtimeMs, gitHead, gitIndex };
+}
+
+function eqMtimes(a: MtimeSnap, b: MtimeSnap): boolean {
+  return a.root === b.root && a.gitHead === b.gitHead && a.gitIndex === b.gitIndex;
+}
+
+function runRgFiles(root: string): Promise<string[]> {
+  return new Promise((resolve, reject) => {
+    execFile('rg', ['--files'], { cwd: root, maxBuffer: 32 * 1024 * 1024 }, (err, stdout) => {
+      if (err) return reject(err);
+      resolve(stdout.split('\n').filter(Boolean));
+    });
+  });
+}