Add gitignore-claude template and wire into registration flows

Introduce scripts/project_rules/gitignore-claude.template with the fleet
pattern that tracks .claude/rules/ while ignoring machine-local Claude state.
ensure_gitignore_claude_rules.py applies it during statehub register,
register_project.sh, and update_agent_instruction_files fleet regen.

statehub_register.py

@@ -20,6 +20,8 @@ STATE_HUB_DIR = Path(__file__).resolve().parent
 API_BASE = os.environ.get("API_BASE", "http://127.0.0.1:8000")
 RULES_TEMPLATES_DIR = STATE_HUB_DIR / "scripts" / "project_rules"
 
+from scripts.ensure_gitignore_claude_rules import ensure_claude_gitignore  # noqa: E402
+
 KEY_CONTEXT_FILES = [
     "INTENT.md",
     "README.md",
@@ -291,6 +293,10 @@ def write_registration_files(
         )
         written.append(brief_path)
 
+    gitignore_path = project_path / ".gitignore"
+    if ensure_claude_gitignore(gitignore_path):
+        written.append(gitignore_path)
+
     return written