feat: add opt-in layered configuration profile (#60)

[codeforester]

Summary

Implements #60 with an opt-in batteries-included configuration profile while preserving the convention-free generic profile.

What changed

• Added CliProfile.batteries_included() with platform-aware user config roots and configurable filenames/directories.
• Added deterministic defaults → user → project → user environment → project environment → explicit file → CLI precedence.
• Added recursive mapping merges, scalar/list replacement semantics, immutable per-key provenance, and environment selection from --environment or base configuration.
• Added typed ConfigSnapshot and FrameworkConfig boundaries; reserved environment, log_level, and keep_temp settings are validated separately from consumer configuration.
• Added Context.framework_config and Context.config_provenance without changing generic profile behavior or existing positional field order.
• Added strict path/name safety, platform config-root helpers, migration documentation, and regression coverage.

Validation

• python -m pytest -q — passed
• mypy --strict examples/typed_consumer.py lib/python/base_cli/config.py lib/python/base_cli/profile.py lib/python/base_cli/context.py — passed
• ./tests/validate.sh — passed
• python -m build --outdir /private/tmp/base-cli-60-dist — sdist and wheel built successfully
• git diff --check — passed

Closes #60