fix: the command whitelist skips the built-in dangerous patterns

[mekjr1]

Fixes #38.

tools.exec.custom_allow_patterns (Config → Run Commands → Command Whitelist) never let a command through. guardCommand checked every deny pattern first and refused any match. It read the allow patterns only for a strict allowlist (allowPatterns) that nothing set.

Now the setting does what its hint says, by the rule the issue suggests:

• ExecTool keeps the built-in deny patterns (denyPatterns) apart from custom_deny_patterns (customDenyPatterns). A command that matches a custom allow pattern skips the built-in patterns. The custom deny patterns apply to every command, so the protection TestShellTool_CustomAllowDoesNotBypassDenyPatterns covers stays: a whitelisted jq still can't read $ENV past a blacklist rule. The workspace limits apply as before.
• The settings page's pattern tester (POST /api/config/test-command-patterns) checks the blacklist first. A command that both lists match shows as blocked; it showed as allowed. The page already shows blocked that way.
• The unused strict allowlist is gone: allowPatterns, SetAllowPatterns and its "not in allowlist" refusal.

A whitelist pattern is matched against the whole command line, as the blacklist is. So ^git\s+push\b also lets whatever is chained after git push skip the built-in patterns. End a pattern with $ to allow a single command.

The whitelist hint now says which patterns a match skips and that the blacklist still applies, in all five languages. docs/use.md lists the whitelist among the command controls. CHANGELOG line.

Tests:

• TestShellTool_CustomAllowPatterns now calls guardCommand. It called Execute without action, which refused before the guard ran. It checks that:
  • a whitelisted command passes a built-in pattern;
  • a command that isn't whitelisted doesn't;
  • a whitelisted command is still refused by a custom deny pattern, or when it leaves the workspace.
• That test fails under both the old rule and a whitelist that skips the custom patterns too. TestShellTool_CustomAllowDoesNotBypassDenyPatterns also fails under the second.
• TestHandleTestCommandPatterns_BlacklistOutranksWhitelist fails with the old tester.

[mekjr1]

Superseded by #63, which includes this change or replaces it.