docs: update READMEs with scheduler changes and TUI/LLM improvements

[bug-ops]

• Root README: replace plain text TUI demo block with ansi-colored confidence bars (green >75%, yellow 40-75%) matching TUI rendering
• zeph-llm: document Claude extended thinking (ThinkingConfig, Extended/ Adaptive variants, --thinking flag, max_tokens auto-bump); expand features table with mock, stt, candle, cuda, metal entries
• zeph-tui: add /schedule command palette entry

Description

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)

Related Issues

Checklist

• My code follows the project's code style guidelines
• I have run cargo +nightly fmt --check and fixed any issues
• I have run cargo clippy --workspace -- -D warnings and addressed all warnings
• I have added tests that prove my fix is effective or that my feature works
• All existing tests pass locally with my changes