Hard-deny: PowerShell patterns + drift-proof the label list

Four new compiled-in hard-deny rules covering PowerShell + cmd.exe
catastrophic patterns (mirror of the POSIX 10):

- Remove-Item / del / rd / ri / rm / erase / rmdir targeting C:\
  or user home / appdata
- Format-Volume / Clear-Disk with any flag (= an invocation, not a
  Get-Help lookup)
- iwr | iex pipe form (PowerShell web-to-execute)
- iex (irm ...) parenthesized form

Universal application — no shell-aware scoping yet. PS cmdlet
identifiers are distinctive enough that bash false-positives are
vanishingly unlikely. Shell-aware policy scoping remains a known
follow-up.

Drift-proof the "Always blocked" label list: backend now exposes
hard_deny_rules() via a new mcp_hard_deny_labels Tauri command, and
PolicyTab loads it at mount instead of hardcoding the list. Avoids
the 11→15 manual sync that would have been needed (and that had
already drifted twice this week).

cargo test --lib: 138 passed; 0 failed (118 prior + 20 new fuzz
cases for rules 11-14; hard_deny_rules_count bumped 10 → 14).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/ipc.ts

@@ -180,6 +180,11 @@ export const mcpPolicyLoad = (): Promise<McpPolicy> =>
 export const mcpPolicySave = (policy: McpPolicy): Promise<void> =>
   invoke("mcp_policy_save", { policy });
 
+/** Compiled-in hard-deny rule labels (the patterns the user CANNOT
+ *  override). Loaded once at PolicyTab mount; backend is the SoT. */
+export const mcpHardDenyLabels = (): Promise<string[]> =>
+  invoke("mcp_hard_deny_labels");
+
 /** Subscribe to MCP action requests from the backend. Each request is a
  *  tool call the frontend must handle (mutate state) and reply to via
  *  {@link mcpActionReply}. */