refactor(github): consolidate types and contents code

[github-actions]

Closes #543

Applied changes based on Issue #543.

I’ve refactored src/github/types.ts and updated its usages in src/github/contents.ts to improve modularity, consistency, and documentation, while preserving all existing functionality:

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1. Extracted & documented reusable payload types

• GitHubComment – a basic issue/PR comment type
• GitHubPullRequestMinimal – a minimal PR shape for review‐comment events
• GitHubReviewComment – extracted the inline shape used by review comments

/**
 * Basic GitHub issue or pull request comment.
 */
export type GitHubComment = { id: number; body: string };

/**
 * Minimal pull request representation for review events.
 */
export type GitHubPullRequestMinimal = Pick<GitHubPullRequest, 'number' | 'title' | 'body'>;

/**
 * GitHub pull request review comment payload.
 */
export type GitHubReviewComment = {
  id: number;
  body: string;
  path: string;
  in_reply_to_id?: number;
  position?: number;
  line?: number;
};

【F:src/github/types.ts†L61-L86】

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2. Updated the review‐comment event to use the new types

export type GitHubEventPullRequestReviewCommentCreated = {
  action: 'created';
  pull_request: GitHubPullRequestMinimal;
  comment: GitHubReviewComment;
};

【F:src/github/types.ts†L88-L94】

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3. Renamed “Github…” types to “GitHub…” for naming consistency

• GithubComment → GitHubComment
• GithubContentsData → GitHubContentsData

-export type GithubComment = { id: number; body: string };
+export type GitHubComment = { id: number; body: string };

 /** Content and comments data for issues and pull requests. */
-export type GithubContentsData = {
+export type GitHubContentsData = {
   content: { number?: number; title: string; body: string; login: string };
   comments: { body: string; login: string }[];
 };

【F:src/github/types.ts†L56-L60】【F:src/github/types.ts†L98-L102】

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4. Updated all references in src/github/contents.ts to the renamed GitHubContentsData

-import type { RepoContext, AgentEvent, GithubContentsData } from './types';
+import type { RepoContext, AgentEvent, GitHubContentsData } from './types';

-export async function getContentsData(
+export async function getContentsData(
   octokit: Octokit,
   repo: RepoContext,
   event: AgentEvent,
-): Promise<GithubContentsData> {
+): Promise<GitHubContentsData> {

... (similarly updated return types on helper functions)

【F:src/github/contents.ts†L6-L7】【F:src/github/contents.ts†L47-L49】【F:src/github/contents.ts†L65-L70】【F:src/github/contents.ts†L124-L129】【F:src/github/contents.ts†L186-L191】

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These changes improve modularity (by extracting reusable type pieces), enforce a consistent naming convention (GitHub vs Github), and add JSDoc for clarity, without altering any runtime behavior. Let me know if you’d like any further tweaks!