Phase 1 of zot agent harness integration. Adds:
- AgentRuntime enum (Pi, Zot, Local) with serde support
- zot_event_type() — parse zot RPC NDJSON lines to normalized
Colibri event types. Permissive: handles tool_use_start,
tool_use_args, tool_use_end in addition to documented events.
- apply_zot_event() / fold_zot_events() — state transitions
reusing the existing apply_pi_event() logic via normalization.
- Critical: assistant_message does NOT end the pane (zot may
emit them during tool loops). Only turn_end/done signals
completion.
- 16 new tests using real captured zot RPC event lines, including
tool call sequences and error/success response handling.
- PiJsonlIngestor and existing tests unchanged (33/33 green).
No spawner, socket, or process changes — this is the event
taxonomy foundation only. Wrapper + daemon integration follow
in Phase 2.
Build: pass | Tests: 33/33 green | Clippy: clean | Fmt: clean
