Add execution-trace viewer

[josephsenior]

Context

Grinta's event ledger records every action during autonomous runs (plans, edits, commands,
failures, recoveries). Currently, this data is only inspectable via raw JSON files.

Proposed solution

Build a lightweight trace viewer that renders the event ledger as a navigable timeline:

• Terminal-based (TUI) viewer using textual or rich
• Show events chronologically with expandable details
• Color-code by event type: plan (blue), edit (green), command (yellow), error (red), recovery (purple)
• Support filtering by event type, file path, or time range
• Allow replaying a segment of the trace

Stretch goals

• HTML export for sharing traces in bug reports
• Side-by-side diff view for edit events
• Integration with grinta benchmark to visualize benchmark runs

Why this matters

Trace inspection is essential for debugging agent behavior and building user trust
in autonomous execution.