fix(#146): reuse resolved doc-map path from early validation in Step 6c

Addresses sonnet/gpt NIT: early validateWorkspacePath call at line 176
discarded the resolved path (using _), then Step 6c called it again.
Store the resolved path in resolvedDocMapFile and reuse it downstream,
eliminating the redundant EvalSymlinks syscall on the happy path.

cmd/review-bot/main.go

@@ -174,11 +174,14 @@ func main() {
 	}
 
 	// Early validation of filesystem-path flags (fail fast before network I/O)
+	var resolvedDocMapFile string
 	if *docMapFile != "" {
-		if _, err := validateWorkspacePath(*docMapFile, "doc-map"); err != nil {
+		resolved, err := validateWorkspacePath(*docMapFile, "doc-map")
+		if err != nil {
 			slog.Error("invalid doc-map path", "error", err)
 			os.Exit(1)
 		}
+		resolvedDocMapFile = resolved
 	}
 
 	// Initialize clients
@@ -365,12 +368,7 @@ func main() {
 	// Step 6c: Load path-scoped design docs if doc-map specified
 	designDocs := ""
 	if *docMapFile != "" {
-		resolvedDocMap, err := validateWorkspacePath(*docMapFile, "doc-map")
-		if err != nil {
-			slog.Error("invalid doc-map path", "error", err)
-			os.Exit(1)
-		}
-		docMapCfg, err := review.ParseDocMapConfig(resolvedDocMap)
+		docMapCfg, err := review.ParseDocMapConfig(resolvedDocMapFile)
 		if err != nil {
 			slog.Error("failed to parse doc-map file", "file", *docMapFile, "error", err)
 			os.Exit(1)