Self-hosted runner now skips context-source repos it can't access instead of failing the whole clone
When a self-hosted runner (the claude runner binary used to run hosted or CI-style pools of sessions) prepares context sources for a session, it used to fail the whole clone if one repo couldn't be reached. Now, if a repo that isn't a work repo (it has no push_targets entry) can't be accessed through the git mount or proxy because of an authentication or permission problem, the runner logs a warning, records the skip as context_source_access_denied, and shows a step message telling the user to check their GitHub connection or ask an admin to check org access.
This keeps one inaccessible repo from blocking an entire session's setup, and it gives users a clear next step (check GitHub access, or ask an admin) instead of an opaque failure.