The seven Map-based caches in WorkspaceGitServiceImpl had no eviction —
the 15s TTL only marked entries stale before refetching in place. Long-
lived daemons accumulated entries for every ephemeral worktree cwd that
ever ran, with checkoutDiffCache holding multi-MB highlighted diffs.
Switch to LRUCache. checkoutDiffCache caps at 64 (heavy values); the
other six aux caches cap at 256. Stale-in-place TTL semantics are
unchanged.
