docs(examples): add dependency markers for all examples

[frant-liu]

Summary

Add lightweight dependency markers to all examples so users can quickly tell whether an example runs locally or requires external services. Closes #58.

Solution Description

Added unified dependency markers (零依赖 / 需 LLM API / 需 OceanBase / 需可选依赖) to every example across all README files under examples/, with a marker legend added at the top of examples/README.md.

Changes:

• examples/README.md

  • Added dependency marker legend table
  • Unified basic / advanced / gis tables to | File | Dependency | Description | format for easy scanning
  • Added missing gis_memory.py and smart_swap.py entries in the gis table
  • Added missing self_evolution_demo.py entry in the advanced table

• examples/basic/README.md

  • Added dependency markers to each section title
  • Fixed langchain_deepagents_example.py dependency info: it requires LangChain + OpenAI API key, previously mislabeled as "no external services"

• examples/advanced/README.md

  • Added dependency markers to each section title
  • Added missing self_evolution_demo.py entry (command, dependency, demo content)

• examples/gis/README.md

  • Replaced English markers (requires OceanBase) with Chinese (需 OceanBase) for consistency

No code changes — documentation only.

[Teingi]

LGTM