Add integration tests for replicate happy paths and --force rejection

Previously replicate coverage at the syncer layer only exercised rejection cases (no-thin target, prune-into-bootstrap). This commit adds the missing green-path tests:

• Overwrites a non-fast-forward branch rewind via relay pack push
• Bootstraps an empty target through the replicate path and carries OperationMode=replicate through the bootstrap result
• Retargets a divergent tag end-to-end against the receive-pack server
• Deletes an orphaned managed ref under --prune alongside an update push, exercising the separate PushCommands delete path
• Rejects --force at session construction before any network I/O, asserting the "use sync instead" guidance text