feat(mcp-server): add 19 platform ops tools — flags.*, jobs.*, maintenance.*, settings.*, webhooks.*
flags (5): list, get, upsert (create-or-update), delete, killSwitch
jobs (4): list, get, trigger, listRuns
maintenance (3): getCurrent (admin full), set, scheduleWindow
settings (3): get, update, checkKillSwitch
webhooks (7): listSubscriptions, create, get, update, delete, listDeliveries, test, rotateSecret
All backed by existing platform-service endpoints — no new backend changes.
MCP server now has 84 tools across 16 namespaces.