feat: warn when a secret-shaped value is found in args instead of env (#1r)

Adds `args_secret_warning(data)` to bcc_core — returns a warning string
when any arg positional value looks like a raw credential (token prefix,
value following a secret-named flag, or URL with embedded user:pass like
postgres://user:pass@host).  `--flag=value` inline forms are intentionally
skipped (the flag name already labels the value).

Adds `secret_warn` QLabel in ServerEditor's stdio page; shown/hidden by
`_check_args()` on every field change, and cleared on deselect or
stdio→remote type switch.  Non-blocking — save path is not touched.

Closes #1

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_core.py

@@ -583,3 +583,55 @@ def test_merge_and_reapply_preserves_both_edits(tmp_path):
     assert result["numStartups"] == 42  # external change preserved
     assert "s2" in result["mcpServers"]  # user's server edit preserved
     assert "s1" not in result["mcpServers"]  # old server replaced
+
+
+# --------------------------------------------------------------------------- #
+# 10 — Secret-in-args warning
+# --------------------------------------------------------------------------- #
+
+
+def test_args_secret_warning_embedded_url_creds():
+    """AC case: postgres://user:pass@host triggers a warning."""
+    data = {"args": ["--connection", "postgres://user:pass@host/db"]}
+    assert c.args_secret_warning(data) is not None
+
+
+def test_args_secret_warning_token_prefix_positional():
+    """A bare ghp_… token as a positional arg triggers a warning."""
+    data = {"args": ["ghp_abc123def456"]}
+    assert c.args_secret_warning(data) is not None
+
+
+def test_args_secret_warning_secret_flag_value_pair():
+    """Value following a secret-named flag triggers a warning."""
+    data = {"args": ["--token", "supersecret"]}
+    assert c.args_secret_warning(data) is not None
+
+
+def test_args_secret_warning_benign_url_no_password():
+    """https:// URL without user:pass should NOT warn."""
+    data = {"args": ["--endpoint", "https://mcp.example.com/sse"]}
+    assert c.args_secret_warning(data) is None
+
+
+def test_args_secret_warning_user_at_host_no_password():
+    """ssh://user@host without a password should NOT warn."""
+    data = {"args": ["ssh://git@github.com"]}
+    assert c.args_secret_warning(data) is None
+
+
+def test_args_secret_warning_inline_flag_value_skipped():
+    """--flag=value inline pairs are self-documenting and should NOT warn."""
+    data = {"args": ["--api-key=sk-abc123"]}
+    assert c.args_secret_warning(data) is None
+
+
+def test_args_secret_warning_env_not_triggered():
+    """Secrets in env (not args) must not trigger args warning, even with benign args present."""
+    data = {"args": ["--verbose"], "env": {"DATABASE_URL": "postgres://user:pass@host/db"}}
+    assert c.args_secret_warning(data) is None
+
+
+def test_args_secret_warning_empty():
+    assert c.args_secret_warning({}) is None
+    assert c.args_secret_warning({"args": []}) is None