behavior: emit tool_started/tool_finished (with args), action_taken, and text_delta from the tool-dispatch boundary

[justrach]

Phase 1 (#246, PR #252) reserves these four kinds but has no producer, so tool name/args never appear even in the local trace and an events-only scorer cannot reconstruct what the agent did. Verified wiring points: the tr.tool call sites at dispatch in exec.zig feed trace.zig's Tracer, which already holds the shared BehaviorTrace pointer.

Constraints from review:

• Rollout order: the deployed collector rejects the reserved kinds (Phase 1 contract), so emitters must be LOCAL-ONLY until zigrepper#143 ships a versioned validation contract for them; the upload projection must skip these kinds regardless of mode until then.
• Privacy design needed before implementation: tool arguments are plaintext in the local file, which changes the documented local privacy posture (docs/behavioral-trajectories.md says automatic events do not include tool arguments). The metadata projection for these kinds is undefined (isMetadataField has no tool-name/args fields): decide class-only vs name vs args per mode.
• Enrich existing emitters at the same time: issue Port schema-harness behavioral trace schema + predict–verify loop into codegraff trajectories #246 wants turn_started to carry task state and run_finished an outcome summary.
• scripts/score_run.py strict profile currently pins producers to the five lifecycle kinds; extend it with the new kinds in the same change.

[justrach]

Shipped on main — f4d7c7c (emit the four reserved kinds under opt-in rich capture) and f67b4e4 (version-agnostic TurnMetrics comptime guard).