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-04.js

@@ -0,0 +1,57 @@
+// Slide 04: Hello world -- first chain with init_chat_model
+// Code slide: the simplest possible working example.
+
+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: 'Hello world',
+    title: 'Первый вызов модели',
+    sectionNumber: 1,
+  });
+
+  ds.helpers.addCodeBlock(slide, pres, theme, {
+    x: 0.5, y: 1.5, w: 6.4, h: 3.25,
+    language: 'python',
+    filePath: 'examples/hello.py',
+    code: [
+      '# Один универсальный инициализатор для всех провайдеров',
+      'from langchain.chat_models import init_chat_model',
+      '',
+      '# Формат: "<provider>:<model>"',
+      'model = init_chat_model("openai:gpt-4.1-mini")',
+      '',
+      '# invoke -> BaseMessage; нам нужен .content',
+      'result = model.invoke("Say hello in one sentence")',
+      'print(result.content)',
+      '',
+      '# >>> "Hello! How can I help you today?"',
+    ].join('\n'),
+  });
+
+  // Right side: explanation card
+  ds.helpers.addCallout(slide, pres, theme, {
+    x: 7.1, y: 1.5, w: 2.4, h: 1.55,
+    kind: 'info',
+    title: 'init_chat_model',
+    text: 'Один фабричный вызов вместо ChatOpenAI / ChatAnthropic / ChatGoogle отдельно.',
+  });
+
+  ds.helpers.addCallout(slide, pres, theme, {
+    x: 7.1, y: 3.2, w: 2.4, h: 1.55,
+    kind: 'success',
+    title: 'Что вернется',
+    text: 'Объект AIMessage: content, response_metadata (usage, model_name), id, tool_calls.',
+  });
+
+  ds.helpers.addSourceLine(slide, pres, theme, {
+    source: 'python.langchain.com/docs/how_to/chat_models_universal_init/',
+  });
+  ds.helpers.addPageNumber(slide, pres, theme, 4);
+}
+
+module.exports = { createSlide };