[Charlie-Qilin]

Why

Partners need to change a managed user's profile, choose the caller ID per session, and set the assistant. This PR adds those calls to the SDK and its docs.

It also fixes a bug: Socket.IO messages sent datetime.now().isoformat() as client_now_date. That value has no UTC offset, so the server could not parse it, and the agent always used UTC.

What changed

Area	Change
Managed users	platform.managed_users.update(external_id, *, email, name, phone, assistant) → PATCH /platform/v1/managed-users/{external_id}. None is not sent; phone="" removes the phone; no arguments sends {}. Errors raise PlatformError.
Assistant	create() and update() take assistant as a dict with identity_id, name or both. Other keys or non-string values raise ValueError before any request. ManagedUser.assistant is ManagedUserAssistant or None.
Caller ID	sessions.get_config() / sessions.update_config(caller_id=...) on GET/PUT /v2/sessions/{id}/config. caller_id is "user" or "platform"; other values raise ValueError before any request. 503 session_config_push_failed is a SessionError; no automatic retry.
Identity catalog	settings.assistant_identities() → GET /v2/app/settings/assistance_identities?identities=catalog. A key-only client reads it anonymously.
client_now_date	Socket.IO chat() and send_message() take it, as REST send_message() already did. On every path it must be an RFC 3339 time with a UTC offset, or ValueError is raised before any request (validate_client_now_date). Without it, nothing is sent.
Sync	PineAI has the same REST methods.

Docs: new sections in sdk-api.md and http-api.md for update, assistant identity (Pine's default assistant until one is chosen), caller ID and the user's time. The REST history delay now says "a minute or more". README links point to the docs on main, so they stay the same across releases and open on PyPI. CHANGELOG has upgrade notes, and the version is 0.5.0rc3.

Breaking

client_now_date without a UTC offset now raises ValueError. The server ignored such values before, so the effect was UTC anyway.

Verification

• ruff check src tests: clean.
• pytest tests --ignore=tests/integration: 271 passed on Python 3.12 and 3.10, 51 of them new.
• mypy: no new errors.
• python -m build and twine check: passed.
• End to end against a local server with the new endpoints, 27/27 passed: create, update and clear a managed user, assistant, catalog, session config, and the errors. The agent received the caller ID setting, the time offset from client_now_date over REST and Socket.IO, no offset without it, and the config change while a session was active.

🤖 Generated with Claude Code

[Charlie-Qilin]

@codex review