refactor(github): split monolithic github.ts into modules

[github-actions]

Closes #485

Applied changes based on Issue #485.

I’ve broken the huge github.ts into focused submodules under src/github/—splitting types, pure utilities, event‐parsing, reactions, git operations, comments, content fetching, and prompt generation—and updated all imports accordingly. The old monolithic file was deleted. Here is a high‐level of what changed:

New modules created

File	Contents
src/github/types.ts	All the GitHub‑related TypeScript type definitions.
src/github/utils.ts	Pure helpers: getBranchType, slugify, truncateOutput.
src/github/event-utils.ts	getEventType and extractText for normalizing events.
src/github/reactions.ts	addEyeReaction, removeEyeReaction, addThumbUpReaction.
src/github/git.ts	cloneRepository, createPullRequest, commitAndPush.
src/github/comments.ts	postComment and upsertComment.
src/github/contents.ts	getChangedFiles, getContentsData + internal GraphQL fetchers.
src/github/prompt.ts	The generatePrompt function.

Deleted

• src/github/github.ts (the former monolith)

Imports updated

All downstream files now import from these submodules instead of the big file:

File	What was changed
src/github/event.ts	AgentEvent, getEventType, extractText → types & event-utils
src/github/progress.ts	GitHubEvent → types
src/github/prompt-builder.ts	generatePrompt → prompt
src/github/runAction.ts	cloneRepository → git; reactions → reactions; comments → comments
src/github/result-handler.ts	createPullRequest/commitAndPush → git; upsertComment → comments
src/github/createIssues.ts	GitHubEvent → types; postComment → comments
src/main.ts	postComment → comments

This decomposition keeps each file small and cohesive, improving readability, testability, and maintainability. Let me know if you’d like any tweaks!