Chore/feature pruning (4/8)

[bnomei]

Linked Issue

Closes #

Description

Reduce dependency footprint by splitting features and pruning unused optional crates. This breaks out CLI, stats, and TUI features, gates the relevant code paths, and removes unused dependencies to keep the library lean. README is updated with the feature matrix and minimal install examples. This is PR 4 of 8 in the intended sequence (1-8).

Type of Change

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

Changes Made

• Split feature flags for CLI, stats, and TUI and gate code paths accordingly.
• Remove unused optional dependencies (syntect, unicode-width).
• Document the feature matrix and minimal install options in the README.

SPEC Compliance

• This PR implements/fixes spec compliance
• Spec section(s) affected:
• Spec version:

Testing

• All existing tests pass
• Added new tests for changes
• Tests cover edge cases and spec compliance

Tests run: cargo test

Pre-submission Checklist

• My code follows the project's coding standards
• I have run code formatting/linting tools
• I have added tests that prove my fix/feature works
• New and existing tests pass locally
• I have updated documentation if needed
• I have reviewed the TOON specification for relevant sections

Breaking Changes

• No breaking changes
• Breaking changes (describe migration path below)

Migration path:

Additional Context

Branch: chore/feature-pruning
Intended PR order: 1-8 (this is PR 4 of 8)