examples: add planning and connectors examples

[saurabhjain1592]

Context

The Go, Rust, and TypeScript SDKs each ship runnable planning and connectors examples, and the Java SDK tracks the same gap in getaxonflow/axonflow-sdk-java#146. The Python SDK's examples/ directory covers decisions, audit, and gateway flows, but has no example for the planning APIs or the connector listing API, even though axonflow/client.py supports both (generate_plan, execute_plan, list_connectors).

What

Add two flat example scripts in the existing house style:

• examples/planning.py - exercises generate_plan and then execute_plan on the returned plan
• examples/connectors.py - exercises list_connectors (read-only; works against a local community stack with no external credentials)

Sibling to imitate

• examples/list_decisions.py in this repo is the template: module docstring listing required env vars, async main() returning an exit code, endpoint from AXONFLOW_AGENT_URL (default http://localhost:8080), credentials from AXONFLOW_CLIENT_ID / AXONFLOW_CLIENT_SECRET.
• For what each example should demonstrate, the Go SDK has runnable siblings at examples/planning/ and examples/connectors/ in getaxonflow/axonflow-sdk-go.

Note: the planning example needs an LLM provider configured on the local stack; say so in the module docstring (the connectors example has no such requirement).

Acceptance criteria

• examples/planning.py exists and runs against a local stack at http://localhost:8080
• examples/connectors.py exists and runs against http://localhost:8080 with no external credentials
• Both follow the docstring and env var conventions of examples/list_decisions.py
• No new dependencies

Happy to help scope or review - questions welcome right here on the thread.