Add an Ollama (local LLM) sample to spring-agent-flow-samples

[ahmed-sekka]

The first-time experience requires a Mistral API key, which is friction for self-hosted / privacy-sensitive evaluators. An Ollama-backed sample removes that barrier.

Acceptance criteria

• spring-ai-starter-model-ollama added as a sample-scoped dependency
• OllamaLocalDemo.java running a small graph against a local Ollama instance
• README sample table updated, with prerequisites note (e.g., ollama pull llama3.2)
• Smoke-tested against Ollama running on the default port

Why

Lowest-barrier evaluation path: clone repo → ollama serve → mvn exec:java. No API key required.