feat(github): expand PR review context

[chubes4]

Summary

• Adds explicit opt-in expanded context to pull_review_context packets without changing the default patch-first shape.
• Fetches full changed-file, optional base-file, and explicit context-path contents through GitHub API helpers with file-count, per-file, and total-character guardrails.

Changes

• Adds expanded_context with separate changed_files, extra_files, skipped, limits, and summary sections.
• Wires fetch-handler settings for include_file_contents, include_base_contents, context_paths, and context size limits.
• Extends the PR review context smoke test to cover default output, explicit expansion, truncation, skipped metadata, total limits, and packet shape separation.

Tests

• php -l inc/Abilities/GitHubAbilities.php && php -l inc/Handlers/GitHub/GitHub.php && php -l inc/Handlers/GitHub/GitHubSettings.php && php -l tests/smoke-github-pr-review-context.php
• php tests/smoke-github-pr-review-context.php
• git diff --check
• homeboy audit data-machine-code --path /Users/chubes/Developer/data-machine-code@feat-pr-review-context-expansion --changed-since origin/main

homeboy lint data-machine-code --path /Users/chubes/Developer/data-machine-code@feat-pr-review-context-expansion was also attempted, but the broad lint currently fails with 352 existing PHPStan findings across GitHubAbilities, Workspace, and smoke tests, including pre-existing undefined-static-method reports for methods present in the same class.

Closes #90

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Drafted the implementation and smoke coverage; Chris remains responsible for review and validation.