Add 122 Python example scripts + .env.example

Each of the 122 code slides now has a standalone .py script in
examples/slide-NNN/script.py with the LLM provider pattern from
bro-js/agents/teacher/assistant/src/angry_teacher/llm.py:
  - load_dotenv() + ChatOpenAI with base_url=https://llm.brojs.ru/v1
  - OPENAI_API_KEY from .env (with safe (or '' or None) pattern)
  - Same comment block with alternative model/base_url choices

Layout:
  - sec1/sec5: code extracted from slide-NN.js (addCodeBlock)
  - sec2/sec3/sec4: code extracted from sectionN.pptx via python-pptx
    (JetBrains Mono font shapes)

100 scripts contain runnable code, 22 are visual-only (dividers,
intro, recap) and just print the slide title.

Setup:
  cp .env.example .env       # fill OPENAI_API_KEY (or symlink to your
                              # teacher/assistant/.env)
  pip install -r requirements.txt
  python examples/slide-005/script.py

requirements.txt

@@ -0,0 +1,23 @@
+# Python deps для examples/*.py
+# Запуск: pip install -r requirements.txt
+# (или uv pip install -r requirements.txt)
+
+# LLM provider (паттерн скопирован из bro-js/agents/teacher/assistant)
+python-dotenv>=1.0.0
+langchain-openai>=0.2.0
+langchain>=1.0.0
+langchain-core>=1.0.0
+
+# LangGraph 1.0 (секция 2)
+langgraph>=1.0.0
+
+# Deep Agents (секция 3)
+deepagents>=0.6.0
+
+# Open SWE (секция 4) — приложение, не pip-пакет; см. github.com/langchain-ai/open-swe
+
+# LangSmith (секция 5)
+langsmith>=0.8.0
+
+# Tooling
+pydantic>=2.0