Expose periodic-schedule catalog management in the Python SDK #501

Python can register periodic tasks via @queue.periodic() (sdks/python/taskito/mixins/decorators.py:496) but cannot manage them afterwards — there is no way to list, unschedule, pause, or resume a registered schedule from the public API.

The native module already exposes all four; only the Python-level wrappers are missing:

• crates/taskito-python/src/py_queue/mod.rs:788,800,807,814 — list_periodic, delete_periodic, pause_periodic, resume_periodic
• sdks/python/taskito/_taskito.pyi:216-219 — already declared on the stub

The other SDKs have shipped this (listPeriodic / deletePeriodic / pausePeriodic / resumePeriodic), so Python is the last one short of the cross-SDK contract.

The docs currently document the gap rather than the feature — docs/content/docs/shared/guides/core/scheduling.mdx:348 says "There's no public API yet to list, pause, or delete a registered schedule" under "Managing periodic tasks", and warns that removing a decorator leaves the schedule firing for a task no worker handles.

Scope

• Add list_periodic() / delete_periodic(name) / pause_periodic(name) / resume_periodic(name) to the appropriate mixin (mixins/inspection.py for the read, mixins/operations.py for the mutations), plus the a* variants in async_support/mixins.py.
• Decide the return shape for list_periodic — the binding currently returns list[tuple[str, str, str, bool]], which is thin next to the PeriodicInfo view the other shells decode (name, task_name, cron_expr, queue, enabled, last_run, next_run, timezone). Widening it is likely the right call.
• Tests under sdks/python/tests/core/, mirroring PeriodicTest.listPauseResumeDelete: list, pause toggles enabled, resume, unknown name → False, delete, double-delete → False.
• Replace the Python-only "no public API yet" block in scheduling.mdx with the real usage, matching the shape of the other SDK blocks in that section.

Found while verifying #485, which turned out to be already implemented.