Define and stabilize base_cli public API exports and docs

[codeforester]

Summary

• Re-export command filters, command protocol helpers, and user configuration types from base_cli.
• Add explicit __all__ declarations for the public command/filter/protocol/history surfaces.
• Add entry-point docstrings for App, Context, and run_app.
• Document the supported facade and add public API regression tests.

Root Cause

Several structured APIs were only reachable through internal-looking module paths, while history implicitly exposed low-level helpers through wildcard import behavior. The main entry points also lacked docstrings for IDE and generated documentation consumers.

Validation

• Focused public API/protocol tests: 63 passed, 4 subtests passed.
• Full Python suite: 1050 passed, 1 skipped, 251 subtests passed.
• Focused Pylint: clean.
• git diff --check.

Fixes #1745