feat: add Microsoft Teams connector

[KrisBraun]

Summary

• New @plotday/connector-ms-teams package syncing Teams channel messages and DMs into Plot
• Two-way sync: replies from Plot post back to Teams channels and DMs
• Real-time updates via Microsoft Graph subscriptions for channel messages; batch sync for DMs
• DMs appear as private threads under a synthetic "Direct Messages" channel

Test plan

• Build: cd connectors/ms-teams && pnpm build compiles cleanly
• Lint: cd connectors/ms-teams && pnpm lint passes
• Auth flow: connect Microsoft account, verify token stored
• Channel discovery: verify teams/channels tree + DM channel appear
• Initial sync: enable a channel, verify last 30 days of messages sync
• DM sync: enable Direct Messages, verify DM conversations appear as private threads
• Write-back: reply to a synced thread, verify reply appears in Teams
• Dedup: reply from Plot, verify no duplicate on sync-back

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