v0.1.91 — TUI tool activity inspector, workspace overview, queued input, safer approvals

TUI overhaul — inspectable tool activity, workspace overview, queued input, and safer approvals:

• /tools — browse the session's tool calls; press Enter to expand a call's arguments and captured result. Compact transcript rows show running / completion / failure, elapsed time, cache status, and output line count — without echoing successful tool output.
• /workspace — workspace path, git branch, context use, tool counts, undo turns available, and whether a follow-up message is queued.
• /sessions <query> — filter sessions by ID or generated title before the browser opens.
• Queued follow-up input — Enter while a turn is running queues one message (a later queued message replaces it); the prompt is only added to the transcript when it actually starts.
• Safer approvals — write approvals now lead with a mutation-specific summary (target path, size, or hunk/file count) before the existing diff; multi-hunk fs_patch review adds a (accept all remaining hunks) and x (reject them).
• Short-terminal modals — settings, models, sessions, skills, checkpoints, and diffs keep the selected content visible with omitted-row markers instead of overflowing.
• Credential-safe settings — saved *_api_key values render as (set; hidden); editing remains an explicit action.

Backed by agent.OnToolResult (post-execution callback with elapsed time) wired through the REPL, TUI, and goal/research/playbook modes.

Unit tests (queued input semantics, bounded modal selection, safe activity summaries, masked keys, approval summaries) + live-smoke-tested the new TUI modals. go test -race clean.