feat(persona): add role-based review personas

Add persona system for specialized review roles. Each persona defines:
- A specific review focus (security, architecture, documentation)
- Custom system prompt additions
- Personality/tone adjustments

Built-in personas: security, architect, docs
Custom personas: load from JSON via persona-file flag

Includes workspace validation to prevent path traversal attacks.

Closes #51

review/formatter.go

@@ -53,3 +53,48 @@ func GiteaEvent(verdict string) string {
 		return "COMMENT"
 	}
 }
+
+// FormatMarkdownWithDisplay formats a ReviewResult with separate display name and sentinel name.
+// displayName is used for the header title, sentinelName is used for the cleanup sentinel.
+// If displayName is empty, sentinelName is used for both.
+func FormatMarkdownWithDisplay(result *ReviewResult, displayName, sentinelName string) string {
+	var sb strings.Builder
+
+	// Use display name for header, or fall back to sentinel name
+	headerName := displayName
+	if headerName == "" {
+		headerName = sentinelName
+	}
+
+	if headerName != "" {
+		title := strings.ToUpper(headerName[:1]) + headerName[1:]
+		sb.WriteString(fmt.Sprintf("# %s Review\n\n", title))
+	}
+
+	sb.WriteString("## Summary\n\n")
+	sb.WriteString(result.Summary)
+	sb.WriteString("\n\n")
+
+	if len(result.Findings) > 0 {
+		sb.WriteString("## Findings\n\n")
+		sb.WriteString("| # | Severity | File | Line | Finding |\n")
+		sb.WriteString("|---|----------|------|------|--------|\n")
+
+		for i, f := range result.Findings {
+			sb.WriteString(fmt.Sprintf("| %d | [%s] | `%s` | %d | %s |\n",
+				i+1, f.Severity, f.File, f.Line, f.Finding))
+		}
+		sb.WriteString("\n")
+	}
+
+	sb.WriteString("## Recommendation\n\n")
+	sb.WriteString(fmt.Sprintf("**%s** — %s\n", result.Verdict, result.Recommendation))
+
+	if sentinelName != "" {
+		sb.WriteString(fmt.Sprintf("\n---\n*Review by %s*\n", headerName))
+		// Hidden sentinel for identifying this bot's reviews during cleanup
+		sb.WriteString(fmt.Sprintf("\n<!-- review-bot:%s -->\n", sentinelName))
+	}
+
+	return sb.String()
+}