chore(shared): add EXCLUDED_DIRS constant for recursive FS scans

Introduces a frozen Set<string> of directory basenames (node_modules, .git,
dist, build, .next, .sisyphus, .omx, .turbo, coverage, out, .cache,
.vscode-test, target, .local-ignore) that callers performing recursive
filesystem scans should skip.

This is shared infrastructure for upcoming fixes in rules-injector,
command-discovery, and claude-code-command-loader that currently descend
into node_modules and other junk directories, causing slow plugin init
and slow edit loops when the plugin is launched in-tree.

src/shared/excluded-dirs.ts

@@ -0,0 +1,18 @@
+const EXCLUDED_DIR_NAMES = [
+  "node_modules",
+  ".git",
+  "dist",
+  "build",
+  ".next",
+  ".sisyphus",
+  ".omx",
+  ".turbo",
+  "coverage",
+  "out",
+  ".cache",
+  ".vscode-test",
+  "target",
+  ".local-ignore",
+] as const
+
+export const EXCLUDED_DIRS: ReadonlySet<string> = Object.freeze(new Set<string>(EXCLUDED_DIR_NAMES))