feat: add optional integration scenarios

[codeforester]

Summary

• Add separate Typer, Rich, and OpenTelemetry learning entry points.
• Keep every integration optional with successful minimal-install fallbacks.
• Add enabled and minimal-path tests plus CI coverage for all three extras.
• Document the adapter boundaries and unchanged machine-output behavior.

Validation

• ./tests/validate.sh
• UV_CACHE_DIR=/private/tmp/base-cli-demo-issue6-uv uv run --extra dev pytest -q (11 passed)
• UV_CACHE_DIR=/private/tmp/base-cli-demo-issue6-uv uv run --extra dev --extra typer --extra rich --extra telemetry pytest -q tests/test_optional_scenarios.py (6 passed)
• Clean minimal wheel environment: 5 passed, 1 skipped
• UV_CACHE_DIR=/private/tmp/base-cli-demo-issue6-uv uv run --with ruff ruff check src tests
• UV_CACHE_DIR=/private/tmp/base-cli-demo-issue6-uv uv run --with ruff ruff format --check src tests

Fixes #6