Improve assistant management for more consistent behavior

[jbencina]

Summary

The main change in this PR is to refactor the initialization of the assistant class such that we are more aligned with the remote state in OpenAI. Instead of locally managing the assistant ID, we now rely on OpenAPI. This should enforce at most a single assistant ID in the user account at any point in time.

Extra commands assistants list and assistants clean were added to help manage the assistants.

Test Plan

Locally ran through multiple scenarios of creating assistants, deleting assistants, and deleting settings to confirm behavior:

• Assistant created if not existing remotely
• Extra assistants pruned if > 1 exists remotely (created manually via OpenAI playground)
• Deleting an active assistant and attempting to chat will automatically create a new one

[Copilot]

Pull Request Overview

This PR refactors assistant initialization to rely on the OpenAI API (removing local assistant ID persistence), adds assistants list and assistants clean CLI commands for remote assistant management, and cleans up related CLI entry points and docstrings.

• Renamed the settings info command to settings show
• Introduced the assistants command group with list and clean subcommands
• Refactored OpenAIClient to unify assistant/thread initialization, remove persisted assistant IDs, and added docstrings across client and handler classes

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/vecsync/cli/settings.py	Renamed info to show and updated registration in settings group
src/vecsync/cli/entry.py	Registered the new assistants command group
src/vecsync/cli/chat.py	Removed the --new-conversation flag and updated function signatures
src/vecsync/cli/assistants.py	Added assistants list and assistants clean commands
src/vecsync/chat/clients/openai.py	Refactored OpenAIClient, added connect/disconnect, cleaned up assistant persistence, and enriched docstrings
src/vecsync/chat/clients/base.py	Introduced Assistant Pydantic model
CHANGELOG.md	Documented the new assistant CLI commands and cleanup behavior

Comments suppressed due to low confidence (2)

src/vecsync/cli/assistants.py:9

• [nitpick] Using list as a function name shadows the built-in list. Consider renaming to list_assistants or explicitly setting @click.command(name='list') to avoid confusion.

def list():