[codex] Modernize README demos and progress ergonomics

[wolph]

Summary

• refresh the README with animated SVG demos and clearer usage examples for labels, totals, live output, and concurrent bars
• place the exact demo code directly under each animated SVG so the rendered output and source stay paired
• render README SVG colors from captured ANSI output so percentage/count colors match the library's real terminal gradient
• show the multiple-bar demo with independently progressing bars instead of synchronized values
• simplify the unknown-length demo to use a straightforward range loop
• remove the extra ergonomics SVG section, generated asset, and obsolete GPG release-verification section
• keep recent log lines visible in the hero SVG while the progress bar advances
• use branch-relative README SVG links so the PR branch renders its own demo assets
• add a repeatable README demo renderer plus tests so documented terminal output stays in sync
• add CLI rate limiting, tighten unit/progress formatting behavior, and harden stream/logging cleanup around failed bars
• isolate stream cleanup tests so stale redirected-output state does not leak between cases
• purge docs/superpowers files from the PR branch history

Validation

• python scripts/render_readme_demos.py --check
• .tox/py313/bin/python -m pytest tests/test_readme_demos.py -q --no-cov
• .tox/py313/bin/python -m pytest -q --no-cov
• .tox/py313/bin/pyright
• .tox/ruff/bin/ruff check scripts/render_readme_demos.py tests/test_readme_demos.py
• .tox/ruff/bin/ruff format --check scripts/render_readme_demos.py tests/test_readme_demos.py
• git diff --check

[gemini-code-assist]

Code Review

This pull request modernizes the progressbar2 library by introducing tqdm-style ergonomic options (such as desc, total, unit, unit_scale, and postfix), adding new Postfix and UnitProgress widgets, and improving print/log coexistence with a reversible logging stream wrapper. It also updates the CLI to support rate limiting and custom display flags, rewrites the README to be demo-led, and adds a script to generate SVG terminal demos. The review feedback identifies three key improvement opportunities: ensuring valid falsy values (like 0 or False) are not omitted in the Postfix widget, wrapping ProgressBarBase.finish in contextlib.suppress during error handling to prevent masking exceptions, and copying logger.handlers to a tuple during iteration to avoid concurrent modification errors.

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