feat(directory): CODEGRAPH_DIR env var to override the index dir name (#636) (#741)

Two environments that share one working tree — most concretely Windows
and WSL — can't safely share a single `.codegraph/`: the daemon lockfile
records a platform-specific pid + socket (named pipe vs Unix socket), and
SQLite locking across the WSL2/Windows filesystem boundary is unreliable,
so two daemons over one index risks corruption.

Add a `CODEGRAPH_DIR` env var (default `.codegraph`) that overrides the
per-project data directory name, so each environment keeps its own index
in the same tree (e.g. `CODEGRAPH_DIR=.codegraph-win` on Windows). The
name is resolved live and validated (rejects separators / `..` / absolute,
falling back to the default with a one-time stderr warning). Indexing and
file-watching now skip ANY `.codegraph-*` sibling so neither side trips
over the other's data.

Routes the previously-hardcoded `.codegraph` literals (db path, lockfile,
error log, watcher ignore, file-scan skip, installer) through the
resolver. No extraction-version bump — index content is unchanged.

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

src/installer/index.ts

@@ -28,6 +28,7 @@ import { getGlyphs } from '../ui/glyphs';
 // installer must stay importable even when native modules can't load).
 import { watchDisabledReason } from '../sync/watch-policy';
 import { isGitRepo, isSyncHookInstalled, installGitSyncHook } from '../sync/git-hooks';
+import { getCodeGraphDir, codeGraphDirName } from '../directory';
 
 // Backwards-compat: keep these named exports — downstream code may
 // import them. The shim in `config-writer.ts` continues to re-export
@@ -362,8 +363,8 @@ export async function runUninstaller(opts: RunUninstallerOptions): Promise<void>
 
   // Step 4: for local uninstall, the index dir is separate — point at
   // `uninit` so the user knows it's still there (and how to remove it).
-  if (location === 'local' && fs.existsSync(path.join(process.cwd(), '.codegraph'))) {
-    clack.log.info('The .codegraph/ index for this project is still here. Run `codegraph uninit` to delete it.');
+  if (location === 'local' && fs.existsSync(getCodeGraphDir(process.cwd()))) {
+    clack.log.info(`The ${codeGraphDirName()}/ index for this project is still here. Run \`codegraph uninit\` to delete it.`);
   }
 
   // Step 5: summary.