chore: extract getRepositoryAccessType method

[hmacr]

Related SER-1170

[greptile-apps]

Greptile Summary

This PR extracts the "find installation access type" logic from searchRepositories into a dedicated getRepositoryAccessType() method on the Adapter base class, and removes the now-redundant $installationId parameter from searchRepositories across both the GitHub and Gitea adapters.

• The refactoring is structurally clean and the new abstract method is well-documented.
• **The fallback value in GitHub::getRepositoryAccessType() was changed from '' (which resolved to false/'selected') to 'all'**, reversing the conservative error-path default from the original code. If the GitHub API call fails or returns an unexpected structure, the method now returns 'all'` instead of implicitly indicating restricted access — this is a silent behavioural regression worth addressing.
• The searchRepositories docblock in GitHub.php still lists the removed $installationId @param entry.
• The new integration test hardcodes 'all' as the expected access type, making it fragile against installation-configuration changes.

Confidence Score: 3/5

• Safe to merge after addressing the fallback-value regression in getRepositoryAccessType().
• The structural refactoring is correct, but changing the fallback from '' to 'all' silently flips the error-path behaviour of searchRepositories from "assume restricted access" to "assume full access", which is a meaningful behavioural change introduced unintentionally during the extraction.
• src/VCS/Adapter/Git/GitHub.php — specifically the fallback value on line 189 of getRepositoryAccessType().

Important Files Changed

Filename	Overview
src/VCS/Adapter.php	Adds abstract getRepositoryAccessType(): string method and removes $installationId from the searchRepositories signature cleanly, with updated docblock.
src/VCS/Adapter/Git/GitHub.php	Implements getRepositoryAccessType() by calling the GitHub App installations API, but the fallback value was changed from '' (conservative/"selected") to 'all' (permissive), altering error-path behavior. The docblock for searchRepositories also retains the now-removed $installationId param entry.
src/VCS/Adapter/Git/Gitea.php	Adds a stub getRepositoryAccessType() that throws Not implemented yet, and removes the unused $installationId parameter from searchRepositories. Both changes are clean.
tests/VCS/Adapter/GitHubTest.php	Adds an integration test for getRepositoryAccessType(), but the assertion hardcodes 'all', making the test brittle and dependent on the live installation's configuration.

_{Reviews (1): Last reviewed commit: "feat: implement `getRepositoryAccessType..." | Re-trigger Greptile}