Update README.MD and add nano-claude-code v3.0 + original-source-code/src

- README.MD: add original-source-code and nano-claude-code sections, update
  overview table (4 subprojects), add v3.0 news entry, expand comparison table
  with memory/multi-agent/skills dimensions
- nano-claude-code v3.0: multi-agent package (multi_agent/), memory package
  (memory/), skill package (skill/) with built-in /commit and /review skills,
  context compression (compaction.py), tool registry plugin system, diff view,
  17 slash commands, 18 built-in tools, 101 tests (~5000 lines total)
- original-source-code/src: add raw TypeScript source tree (1884 files)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

nano-claude-code/skill/__init__.py

@@ -0,0 +1,14 @@
+"""skill package — reusable prompt templates (skills)."""
+from .loader import (  # noqa: F401
+    SkillDef,
+    load_skills,
+    find_skill,
+    substitute_arguments,
+    register_builtin_skill,
+    _parse_skill_file,
+    _parse_list_field,
+)
+from .executor import execute_skill  # noqa: F401
+
+# Importing builtin registers the built-in skills
+from . import builtin as _builtin  # noqa: F401