docs: fix stale safe-outputs.memory references and document McpOptions.enabled

[Copilot]

Two documentation drift issues found by the weekly audit: stale references to the removed safe-outputs.memory key (memory moved to tools.cache-memory) and a completely undocumented enabled: false MCP toggle.

Stale clearMemory injection trigger (AGENTS.md)

Two places incorrectly attributed the auto-injected clearMemory parameter to safe-outputs.memory; corrected to tools.cache-memory to match the actual check in src/compile/common.rs.

Document McpOptions.enabled (AGENTS.md, README.md, prompts/create-ado-agentic-workflow.md)

The enabled: false field — which silently skips an MCP entry at compile time without requiring deletion — was absent from all user-facing docs. Added to the Configuration Properties section in AGENTS.md, as a comment in the README.md YAML example, and in Step 8 of the prompt template:

mcp-servers:
  my-tool:
    container: "node:20-slim"
    enabled: false   # temporarily disable without removing the entry
    allowed:
      - do_thing