Fix bd-fwul: Add executable bit validation for git hooks

Added validation to hooksInstalled() to check if hook files have the
executable bit set. Previously we only checked for file existence and
marker strings, which meant hooks could appear installed but fail
silently if they weren't executable.

The fix adds Mode().Perm() & 0111 checks for both pre-commit and
post-merge hooks after verifying their content.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

cmd/bd/init.go

@@ -421,6 +421,23 @@ func hooksInstalled() bool {
 		return false
 	}
 
+	// Verify hooks are executable
+	preCommitInfo, err := os.Stat(preCommit)
+	if err != nil {
+		return false
+	}
+	if preCommitInfo.Mode().Perm()&0111 == 0 {
+		return false // Not executable
+	}
+
+	postMergeInfo, err := os.Stat(postMerge)
+	if err != nil {
+		return false
+	}
+	if postMergeInfo.Mode().Perm()&0111 == 0 {
+		return false // Not executable
+	}
+
 	return true
 }