feat(admin): add machine size update endpoint and admin UI

[evanjacobson]

Summary

• Adds a targeted PATCH /api/platform/machine-size endpoint to update a kiloclaw instance's machineSize without re-provisioning (which would wipe envVars, secrets, etc.)
• Adds updateMachineSize DO method, internal client method, and tRPC admin mutation through the full stack
• Adds Machine Size editor in the admin panel's Live Worker Status card with valid Fly.io machine configurations (shared-cpu-2x minimum, 3 GB RAM minimum)
• Memory options are dynamically computed based on cpu_kind and CPU count, respecting Fly's step size and per-preset min/max rules

Test plan

• Verify pnpm tsc --noEmit passes in both kiloclaw/ and root
• Test the admin UI: open an instance detail, verify Machine Size displays correctly
• Test editing: changing CPU Kind auto-adjusts CPU and memory options
• Test Save: confirm mutation succeeds and toast shows "Takes effect on next restart"
• Test Reset to Default: confirm sends null and displays "Default (shared-cpu-2x / 3 GB)"
• Verify new size is applied after a machine restart (via guestFromSize)