feat(connector): add Calendly data-source connector

[1nkspand]

Description

Adds a Calendly data-source connector under packages/connector/calendly/, following the shape of the
five existing connectors (Notion is the closest working reference).

What it does

Turns your scheduled events into memory — "ask my calendar". Each active event becomes a document
whose content includes the event name and timing, the meeting notes, and — most importantly — every
invitee's questions & answers (the custom-question responses given at booking, which carry the
actual context).

Design

• Auth — Calendly Personal Access Token, sent as Authorization: Bearer. Read-only (three GET
  endpoints: current user, list events, list invitees).
• Ingest — events flow through cognee's document-mode path (DOCUMENT_SOURCE_ATTR), so they go
  through the normal cognify entity-extraction pipeline rather than the relational dlt-row path.
• Incremental sync — updated_at-based cursor, mirroring the Confluence connector. Each run does
  a cheap metadata sweep of active events and re-fetches only those whose updated_at advanced since
  the last run (plus anything new to the corpus). Because the cursor is updated_at, not start_time,
  a meeting note added after an event ends is picked up on the next sync.
• Forget-on-delete — Calendly has no delete feed, so each run compares the ids it saw last run
  against the current active sweep. A canceled (or vanished) event drops out of the active listing and
  is emitted with the _deleted hard-delete marker; dlt removes it on merge and cognee's existing
  orphan_cleanup purges it from the graph + vector + relational stores.

Files

• cognee_community_connector_calendly/calendly.py — the dlt resource + sync state machine +
  minimal Calendly API client
• cognee_community_connector_calendly/__init__.py — public calendly_source export
• README.md — setup steps, usage, and sync/forget-on-delete semantics
• examples/example.py — runnable end-to-end demo
• tests/test_calendly.py — 19 tests
• pyproject.toml, uv.lock — package metadata + locked deps

Testing

uv run pytest tests/ — 19 tests, no live token/network required (the Calendly API is fully mocked).
Coverage:

• event/invitee rendering (meeting notes + invitee Q&A are the core context)
• pagination across list_events / list_invitees
• full backfill, the updated_at incremental cursor, meeting notes added to a past event, cancel /
  vanish → tombstone, invitee-email scoping
• the dlt resource wiring (merge + id PK + hard_delete column + document-mode marker)
• an offline dlt-merge e2e proving a cancel marker physically removes the row

Closes #4816

DCO Affirmation

I affirm that all code in every commit of this pull request conforms to the terms of the Topoteretes Developer Certificate of Origin.