Show live per-agent progress during parallel runs

[that-github-user]

Problem

After thinktank run starts agents, the terminal goes silent for 5–20 minutes. The only feedback is a single line: "Running N agents in parallel (claude-code)...". With --verbose the raw agent output floods the terminal. There is no middle ground.

Users have no way to know:

• Which agents are still running vs. finished
• Whether an agent is stuck or making progress
• How long until the run completes

Proposed Solution

Add a live status panel that updates in-place (using ANSI cursor movement) showing per-agent state:

Running 5 agents in parallel (claude-code, sonnet)...

  Agent 1  ██████████████████░░  running   1m 23s
  Agent 2  ████████████████████  done      1m 10s  ✓ tests passed
  Agent 3  ████████████████████  done      1m 45s  ✗ tests failed
  Agent 4  ██████░░░░░░░░░░░░░░  running     42s
  Agent 5  ████░░░░░░░░░░░░░░░░  running     28s

States: waiting, running, done, timeout, error

When NO_COLOR or non-TTY, fall back to a simple log-style output:

[1m 23s] Agent 1: still running...
[1m 10s] Agent 2: complete (tests passed)

Acceptance Criteria

• Status panel renders live in a TTY, updating every ~2 seconds without scrolling
• Shows per-agent elapsed time and current state
• Shows test result (pass/fail) as each agent finishes
• Falls back to plain log output when NO_COLOR is set or stdout is not a TTY (e.g., CI)
• --verbose still dumps raw agent output (current behavior preserved for debugging)
• No additional runtime dependencies introduced

[that-github-user]

Fixed in #128. Live per-agent progress updates during runs. TTY: per-line updates. Non-TTY: simple counter. 11 new tests. Generated by thinktank Opus (5/5 pass).