Detect non-TTY output and add --no-color / --output-format flags

[that-github-user]

Problem

thinktank always emits ANSI color codes and Unicode box-drawing characters regardless of whether stdout is a terminal. When output is piped to a file, CI log aggregator, or grep, the result is unreadable garbage:

\x1b[1m\x1b[36m══ Ensemble Results ══\x1b[0m

Proposed solution

1. TTY detection: wrap all color calls in a check — if !process.stdout.isTTY, strip colors and replace Unicode box-drawing with ASCII equivalents (already partially done for Windows in Add ANSI color support detection for Windows cmd.exe compatibility #27, but TTY detection is separate)
2. --no-color flag: explicit opt-out (also honour NO_COLOR=1 env var per https://no-color.org/)
3. --output-format flag: text (default), json
   • json mode: emit a single JSON object to stdout containing the full EnsembleResult so scripts can process results programmatically
   • text mode: current human-readable output

Acceptance criteria

• When stdout is not a TTY, colors are stripped automatically
• NO_COLOR=1 thinktank list produces plain text
• --no-color flag works
• --output-format json prints the full result as a JSON object (matches EnsembleResult schema)
• --output-format json is consistent for run, list, stats, and compare
• Tests verify plain-text and JSON output modes

[that-github-user]

Fixed in #114. Added --no-color and --output-format json flags. Generated by thinktank Opus (Copeland: #2 at +2).