Initial commit: LangChain evolution tutorial deck (132 slides)

- Cover, TOC, 5 dividers, 3 recap slides
- 5 sections (chains, langgraph, deepagents, openswe, ecosystem)
- design-system.js with theme tokens + 9 helper functions
- research/: timeline + sources + per-tech notes
- final-compile.js + merge.js for rebuild pipeline
- output/: langchain-evolution.pptx (2.3 MB) + langchain-evolution.pdf (1.1 MB) + 7 sample previews

slides/section1-chains/slide-05.js

@@ -0,0 +1,52 @@
+// Slide 05: ChatModels -- provider routing through init_chat_model
+// Code slide: how to switch providers without changing call sites.
+
+const ds = require('./design-system');
+
+function createSlide(pres, theme) {
+  const slide = pres.addSlide();
+  ds.helpers.slideBase(slide, pres, theme);
+
+  ds.helpers.addHeader(slide, pres, theme, {
+    eyebrow: 'STAGE 1: CHAINS',
+    section: 'ChatModels',
+    title: 'Переключение провайдера -- одна строка',
+    sectionNumber: 1,
+  });
+
+  ds.helpers.addCodeBlock(slide, pres, theme, {
+    x: 0.5, y: 1.5, w: 9.0, h: 3.25,
+    language: 'python',
+    filePath: 'examples/multi_provider.py',
+    code: [
+      'from langchain.chat_models import init_chat_model',
+      '',
+      '# OpenAI',
+      'm_openai = init_chat_model("openai:gpt-4.1-mini")',
+      '',
+      '# Anthropic',
+      'm_anthropic = init_chat_model("anthropic:claude-3-7-sonnet-latest")',
+      '',
+      '# Google Vertex AI',
+      'm_google = init_chat_model("google_vertexai:gemini-2.0-flash")',
+      '',
+      '# Все три -- объекты BaseChatModel. Один и тот же .invoke()',
+      'for m in [m_openai, m_anthropic, m_google]:',
+      '    print(type(m).__name__, ":", m.invoke("ping").content[:30])',
+    ].join('\n'),
+  });
+
+  // Bottom callout -- env vars
+  ds.helpers.addCallout(slide, pres, theme, {
+    x: 0.5, y: 4.85, w: 9.0, h: 0.3,
+    kind: 'warning',
+    text: 'Нужны API-ключи в env: OPENAI_API_KEY / ANTHROPIC_API_KEY / GOOGLE_API_KEY -- провайдер-пакет сам их подхватит.',
+  });
+
+  ds.helpers.addSourceLine(slide, pres, theme, {
+    source: 'python.langchain.com/docs/concepts/chat_models/',
+  });
+  ds.helpers.addPageNumber(slide, pres, theme, 5);
+}
+
+module.exports = { createSlide };