Problem

Currently all tools are always included in the system prompt tool catalog. Tools with deny-all rules should be hidden from the LLM to prevent it from attempting to use them.

Solution

• ToolRegistry::format_for_prompt() accepts &PermissionPolicy
• Tools where all rules resolve to Deny are excluded from the prompt
• Tools with mixed rules still appear (LLM should try, permission check handles it)

Acceptance Criteria

• Denied tools excluded from system prompt
• Partially denied tools still visible
• Test for prompt generation with permission filtering

Part of #247 (M19 Phase C)