Refactor: replace octokit with @octokit/rest, fix injection and dead code

- Replace heavy `octokit` package with `@octokit/rest` + `@octokit/graphql`
  (bundle: 8,828 -> 4,007 lines)
- Fix GraphQL injection: use parameterized variables instead of string
  interpolation for minimizeComment mutation
- Remove dead `body` null-coalescing logic (`let body = null; body ??= ...`
  simplified to `const body = ...`)
- Hoist warningRegex/errorRegex out of the loop
- Replace hand-rolled CompositeKeyMap/groupBy with Map and Map.groupBy
- Normalize all variable names to camelCase
- Remove no-op runnerEnvironment check in worker

https://claude.ai/code/session_01NpiSv9DJeWXyK77tjPGt8F

Author: claude