feat(runner): inline raw event payload into agent prompt

[DominikPinsel]

Summary

The runner only prompted agents with a minimal <event> summary block:

<event>
  type: issue_comment.created
  org: DominikPinsel
  repo: DominikPinsel/ainsel
  issue: 83
  actor: DominikPinsel
  event_id: evt_...
</event>

even though the hub already delivered the full webhook payload in task.payload. Comment bodies, issue titles/bodies and all other event details never reached the model, so e.g. a @review-agent wdyt? mention left the agent blind to what it was supposed to review.

Changes

• buildUserMessage now appends the raw payload as a pretty-printed <event-data> JSON block after the event summary
• Capped via new EVENT_DATA_MAX_CHARS env (default 16,000 chars), truncated head+tail with the existing truncateWithMarker
• Added EVENT_DATA_MAX_CHARS to the transcript-redaction denylist (non-sensitive config)
• Chat/cron branches unchanged — they already carry their content inline

Notes

No payload filtering: whatever the webhook delivered is inlined (subject to the char cap). Payload content goes into the prompt, not the transcript store.

Test plan

• npm test in pi/pi-extensions/ainsel-runner — 83/83 pass (10 new tests: payload inlining, null/chat omission, truncation marker, resolveEventDataMaxChars default/invalid/valid)
• Deploy runner, comment @agent on a PR, verify the prompt contains the full event JSON