fix(examples): use environment variables for LLM config in hello world

Allow hello world example to use the same LLM_API_KEY and LLM_BASE_URL
environment variables as other examples, enabling consistent configuration
across all examples.

Changes:
- Use os.getenv() for model with default 'openhands/claude-sonnet-4-5-20250929'
- Add base_url parameter from LLM_BASE_URL environment variable
- Add usage_id for better tracking
- Add comments about API key configuration

Author: jpshackelford

examples/01_standalone_sdk/01_hello_world.py

@@ -6,8 +6,13 @@
 from openhands.tools.terminal import TerminalTool
 
 
+# Credits for Claude Sonnet 4.5 model are available at
+# https://app.all-hands.dev/settings/api-keys
+# For Anthropic or others use LiteLLM model names, e.g.
+# LLM_MODEL="anthropic/claude-sonnet-4-5-20250929"
+
 llm = LLM(
-    model="anthropic/claude-sonnet-4-5-20250929",
+    model=os.getenv("LLM_MODEL", "openhands/claude-sonnet-4-5-20250929"),
     api_key=os.getenv("LLM_API_KEY"),
 )