feat(cli): add option to hide the startup banner

[konsisumer]

What changed and why

• Supersedes closed feat(cli): add display.show_banner option for minimal startup #23679 with its display.show_banner option for the classic CLI. Set display.show_banner: false to clear the screen without rendering the startup or /clear banner; diagnostic warnings continue to appear.
• Adds display.show_banner: true to the shared DEFAULT_CONFIG, so fresh, setup, and reset configurations resolve the documented default consistently.
• Adds coverage for full and compact banner suppression, /clear, and the shared config default.

How to test

• Run pytest tests/cli/test_cli_show_banner_option.py tests/cli/test_cli_context_warning.py -q -x --timeout=60.
• Run pytest tests/ -q -x --timeout=60.
• Start the classic CLI with display.show_banner: false and run /clear; the screen clears without the banner while warnings are still rendered.

What platforms tested on

• macOS (Darwin)

Fixes #23487

[teknium1]

Thanks for carrying forward #23679 and adding the shared default that its discussion identified as missing. The feature premise remains valid on current main: cli.py:7051-7081 always renders the startup banner, and the prompt-toolkit /clear redraw independently renders one at cli.py:9639-9659.

Problems

• cli-config.yaml.example:1264 and PR cli.py:4165 say the option applies on /new. On current main, /new only calls new_session() (cli.py:9744-9757); /clear is the command that clears and redraws the banner (cli.py:9614-9674). This should be documented as /clear.

Suggested changes

• Replace /new with /clear in those two new comments. The implementation correctly gates both the ordinary show_banner() path and the separate prompt-toolkit /clear path, while retaining the diagnostic code after the visual-banner guard.

Automated hermes-sweeper review.

[teknium1]

/new only rotates the session; it does not redraw a banner. The redraw path this option gates is /clear (cli.py:9614-9674 on current main), so please name /clear here.

[konsisumer]

Thanks for the review. Addressed in this push:

• Command reference: corrected both new show_banner comments to document the startup and /clear banner paths, rather than /new.

Validation: ruff check on changed Python files; focused CLI tests (16 passed); full test suite passed.

[konsisumer]

Rebased onto current origin/main and resolved the cli.py conflict by retaining main's banner-snapshot path under display.show_banner. Corrected the formatter-required test layout.

Focused CLI tests passed (13 passed); changed-file Ruff and Windows-footgun checks passed. The bounded full suite was started but did not return a usable completion record in this environment.

The 5-file, 456-line diff remains the original feature scope: the 209-line new test file was pre-existing PR content, and the extra cli.py churn is necessary to rebase the guard around main's refactored banner method.