fix(security): strip shell escapes in denylist normalizer; fail-closed on missing approval module

DANGEROUS_PATTERNS and HARDLINE_PATTERNS are matched on the raw command string,
so backslash-escape (r\m) and empty-quote split (r''m) bypass both lists.
_normalize_command_for_detection now strips these before pattern matching.

tui_gateway shell.exec had a bare 'except ImportError: pass' that silently
disabled the entire safety gate if tools.approval wasn't importable. Changed
to fail-closed (return 5001 error). Added detect_hardline_command check.

Fixes #36846, #36847.

tui_gateway/server.py

@@ -8490,15 +8490,20 @@ def _(rid, params: dict) -> dict:
     if not cmd:
         return _err(rid, 4004, "empty command")
     try:
-        from tools.approval import detect_dangerous_command
+        from tools.approval import detect_dangerous_command, detect_hardline_command
 
+        is_hardline, hardline_desc = detect_hardline_command(cmd)
+        if is_hardline:
+            return _err(
+                rid, 4005, f"blocked (hardline): {hardline_desc}. Use the agent for dangerous commands."
+            )
         is_dangerous, _, desc = detect_dangerous_command(cmd)
         if is_dangerous:
             return _err(
                 rid, 4005, f"blocked: {desc}. Use the agent for dangerous commands."
             )
     except ImportError:
-        pass
+        return _err(rid, 5001, "shell.exec unavailable: approval safety module not importable")
     try:
         r = subprocess.run(
             cmd, shell=True, capture_output=True, text=True, timeout=30, cwd=os.getcwd()