Adds the typed interception contexts (`crewai/hooks/contexts.py`) and wires
the `execution_start`, `input`, `output`, and `execution_end` points for both
crews and flows through the dispatcher. `prepare_kickoff` and
`Flow.kickoff_async` fire `execution_start`/`input` so a hook can rewrite
resolved inputs before the run, while `Crew._create_crew_output` and the flow
tail fire `output`/`execution_end` so the final result can be observed or
replaced. Closes the eight critical-path points without touching the legacy
hooks.
