fix(postinstall): handle broken symlinks during npm install

When upgrading from older CCS versions, ~/.ccs/shared/* directories may
exist as broken symlinks (dangling symlinks pointing to deleted targets).

Problem:
- fs.existsSync() returns false for broken symlinks
- fs.mkdirSync() fails with ENOENT because path exists as broken symlink

Solution:
- Added removeIfBrokenSymlink() helper that detects and removes dangling
  symlinks using lstatSync (doesn't follow symlinks) + statSync (follows)
- Applied to shared directory and all subdirectories before mkdir

Fixes npm install error: ENOENT: no such file or directory, mkdir

scripts/postinstall.js

@@ -24,6 +24,35 @@ function getCcsHome() {
   return process.env.CCS_HOME || os.homedir();
 }
 
+/**
+ * Check if path is a broken symlink and remove it if so
+ * Fixes: ENOENT error when mkdir tries to create over a dangling symlink
+ * @param {string} targetPath - Path to check
+ * @returns {boolean} true if broken symlink was removed
+ */
+function removeIfBrokenSymlink(targetPath) {
+  try {
+    // lstatSync doesn't follow symlinks - it checks the link itself
+    const stats = fs.lstatSync(targetPath);
+    if (stats.isSymbolicLink()) {
+      // Check if symlink target exists
+      try {
+        fs.statSync(targetPath); // This follows symlinks
+        return false; // Symlink is valid
+      } catch {
+        // Target doesn't exist - broken symlink
+        fs.unlinkSync(targetPath);
+        console.log(`[!] Removed broken symlink: ${targetPath}`);
+        return true;
+      }
+    }
+    return false;
+  } catch {
+    // Path doesn't exist at all
+    return false;
+  }
+}
+
 /**
  * Validate created configuration files
  * @returns {object} { success: boolean, errors: string[], warnings: string[] }
@@ -85,6 +114,8 @@ function createConfigFiles() {
 
     // Create ~/.ccs/shared/ directory structure (Phase 1)
     const sharedDir = path.join(ccsDir, 'shared');
+    // Handle broken symlinks (common when upgrading from older versions)
+    removeIfBrokenSymlink(sharedDir);
     if (!fs.existsSync(sharedDir)) {
       fs.mkdirSync(sharedDir, { recursive: true, mode: 0o755 });
       console.log('[OK] Created directory: ~/.ccs/shared/');
@@ -94,6 +125,8 @@ function createConfigFiles() {
     const sharedSubdirs = ['commands', 'skills', 'agents', 'plugins'];
     for (const subdir of sharedSubdirs) {
       const subdirPath = path.join(sharedDir, subdir);
+      // Handle broken symlinks before creating directory
+      removeIfBrokenSymlink(subdirPath);
       if (!fs.existsSync(subdirPath)) {
         fs.mkdirSync(subdirPath, { recursive: true, mode: 0o755 });
         console.log(`[OK] Created directory: ~/.ccs/shared/${subdir}/`);