Generate CLI docs from argparse and add CI verification

[MicheleBonus]

Motivation

• Prevent divergence between the CLI implementation and the docs by deriving help text directly from the parser.
• Make ambermeta/cli.py::build_parser() the single source of truth for global and per-command options.
• Remove or correct hand-maintained/unsupported TUI option docs by reflecting the real parser output.

Description

• Added scripts/export_cli_help.py, which imports build_parser(), renders format_help() for the root parser and subcommands, and injects those help blocks into docs/cli.md between markers like <!-- BEGIN_CLI_HELP:plan -->/<!-- END_CLI_HELP:plan -->.
• Reworked docs/cli.md to embed generated help blocks for root, plan, init, validate, info, tui, and gui, replacing several hand-maintained tables and correcting the documented TUI options to match the parser.
• Added a CI workflow .github/workflows/cli-docs-sync.yml that runs python scripts/export_cli_help.py --check and fails the job when the generated help differs from the committed docs.
• The script supports a --check mode that exits non-zero when docs/cli.md is out of date and a normal mode that updates the file in-place.

Testing

• Ran python scripts/export_cli_help.py to generate/update docs/cli.md, which completed successfully and updated the docs as expected.
• Ran python scripts/export_cli_help.py --check which reported the docs are up to date and exited 0.
• Ran pytest -q tests/test_cli_init.py tests/test_cli_protocol_output.py and observed all tests passed (7 passed).

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Codex Task