docs: reorganize into en/ and bg/ subfolders with numbered indices

- New docs/index.md with language selector
- docs/en/ — 01-getting-started, 02-architecture, 03-ai-integration,
  04-api-reference, 05-user-guide, 06-roadmap
- docs/bg/ — same structure in Bulgarian
- Root README.md trimmed to quick-start + links to docs/
- Removed old flat docs/ files (ARCHITECTURE.md, AI_FIRST.md, etc.)
- Added swap!/reset! examples to getting-started guides

docs/index.md

@@ -0,0 +1,16 @@
+# Clojure/Nim Documentation
+
+> A Clojure dialect that compiles to Nim → C → native binaries.
+
+## Choose Language / Избор на език
+
+| 🇬🇧 English | 🇧🇬 Български |
+|------------|-------------|
+| [English Documentation](en/index.md) | [Българска Документация](bg/index.md) |
+
+## Quick Links
+
+- **GitHub/GitLab:** [lisp-nim](https://gitlab.com/balvatar/lisp-nim)
+- **Build:** `make build && make check`
+- **Tests:** 276+ tests across 8 test suites
+- **AI Integration:** DeepSeek API, OpenAI-compatible, Xiaomi MiMo