Unified connector: branches sync but pull requests and commits never appear in Development panel

## Summary

The Development panel receives **branch/ref** data but never **pull request** or **commit** data. Ref ingestion works (including deletions, in real time); PR and commit ingestion never happens.

This looks similar in shape to #715 (a server-side sync incident), but affects PRs/commits specifically while branches are fine.

## Environment

- App: **GitHub for Atlassian** (unified connector), v2.3.0
- Jira Cloud site (redacted), GitHub org + repo: single private repo, org-level install
- GitHub App permissions: **read/write on pull requests**, **All repositories**
- Backfill status: **FINISHED**; re-running backfill changed nothing
- No legacy DVCS connection (Jira → Settings → System → **DVCS accounts is empty**)

## What works (rules out connection / webhooks / permissions)

- A branch whose name contains the issue key appeared under the issue.
- **Deleting** that remote branch was reflected in Jira **in real time** → webhooks are delivered and processed.

## What doesn't

- A PR with the issue key in its **title**, **source branch name**, and **body** never appeared in the Development panel — across a **reopen** event and a later **merge** event (multiple live `pull_request` events fired).
- The **merge commit on the default branch** references the issue key — also absent.
- **No commits appear at all**, even after merge to the default branch.

## Expected

PR (key in title) and commits on the default branch (key in message) should appear in the issue's Development panel, as branches do.

## Actual

Only branches (and their deletion) sync. PRs and commits never do.

## Notes

- I'm aware the merge commit used `Closes #CS-19` (hash-prefixed), which historically broke key detection per #189 (fixed by #213). But the **PR title used a clean, unprefixed key** and still didn't surface — so the `#` prefix is not the cause here.
- Ref pipeline works; PR/commit pipeline does not. Requesting investigation into PR/commit ingestion into the Development panel for the unified connector.

Start with unified connector webhook handling for pull_request events, then compare the branch/ref, pull-request, and commit ingestion paths and the completed backfill. Done means a PR identified by its title or source branch and a commit on the default branch appear in the Jira Development panel, while branch deletion behavior remains intact.

Written by the indexing model from the issue text.