fix(watcher): bound fd/watch cost with a native fs.watch hybrid (#644, #496, #555, #628, #579) (#650)

chokidar v4 holds one OS file descriptor per watched file on macOS (libuv's
kqueue backend registers an fd per vnode; fsevents is installed but v4 no
longer uses it). On a large project the `serve --mcp` daemon accumulated tens
of thousands of open REG descriptors and exhausted kern.maxfiles — crashing
unrelated processes system-wide with ENFILE. #276 only trimmed the count by
ignoring directories; the source tree still cost one fd per file.

Replace chokidar with a pure-JS native fs.watch hybrid, keeping codegraph's
zero-native-addon "any OS builds any bundle" invariant:

  - macOS / Windows: a single recursive fs.watch (one FSEvents stream /
    ReadDirectoryChangesW handle) -> O(1) descriptors regardless of repo size.
  - Linux: one inotify watch per directory (O(dirs), dynamic add for new
    dirs, capped via CODEGRAPH_MAX_DIR_WATCHES) instead of per-file watches.

Validated empirically: macOS 0 extra fds at 6k and 12k files; Linux 31 inotify
watches at 6k files (per-file would be 6k); Windows recursive catches nested
and new-directory edits. Full test suite green.

Tests drive the watcher through an inertForTests seam (no OS watcher) for
determinism under parallel vitest, with one real-fs end-to-end test exercising
the genuine native path.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

package-lock.json

@@ -10,7 +10,6 @@
       "license": "MIT",
       "dependencies": {
         "@clack/prompts": "^1.3.0",
-        "chokidar": "^4.0.3",
         "commander": "^14.0.2",
         "fast-string-width": "^3.0.2",
         "fast-wrap-ansi": "^0.2.0",
@@ -1005,21 +1004,6 @@
         "node": ">= 16"
       }
     },
-    "node_modules/chokidar": {
-      "version": "4.0.3",
-      "resolved": "https://registry.npmjs.org/chokidar/-/chokidar-4.0.3.tgz",
-      "integrity": "sha512-Qgzu8kfBvo+cA4962jnP1KkS6Dop5NS6g7R5LFYJr4b8Ub94PPQXUksCw9PvXoeXPRRddRNC5C1JQUR2SMGtnA==",
-      "license": "MIT",
-      "dependencies": {
-        "readdirp": "^4.0.1"
-      },
-      "engines": {
-        "node": ">= 14.16.0"
-      },
-      "funding": {
-        "url": "https://paulmillr.com/funding/"
-      }
-    },
     "node_modules/commander": {
       "version": "14.0.3",
       "resolved": "https://registry.npmjs.org/commander/-/commander-14.0.3.tgz",
@@ -1285,19 +1269,6 @@
         "node": "^10 || ^12 || >=14"
       }
     },
-    "node_modules/readdirp": {
-      "version": "4.1.2",
-      "resolved": "https://registry.npmjs.org/readdirp/-/readdirp-4.1.2.tgz",
-      "integrity": "sha512-GDhwkLfywWL2s6vEjyhri+eXmfH6j1L7JE27WhqLeYzoh/A3DBaYGEj2H/HFZCn/kMfim73FXxEJTw06WtxQwg==",
-      "license": "MIT",
-      "engines": {
-        "node": ">= 14.18.0"
-      },
-      "funding": {
-        "type": "individual",
-        "url": "https://paulmillr.com/funding/"
-      }
-    },
     "node_modules/rollup": {
       "version": "4.57.1",
       "resolved": "https://registry.npmjs.org/rollup/-/rollup-4.57.1.tgz",