runtime: add config switches for memory and embeddings

[CastleOneX]

Problem

OpenFang did not have an explicit runtime-level way to disable memory entirely or disable embedding-backed recall independently. In practice, memory behavior could still partially activate unless provider setup failed in a particular way, which led to unnecessary embedding initialization attempts, noisy fallback paths, and avoidable external calls.

What this changes

• Adds explicit config flags in crates/openfang-types/src/config.rs:
  • memory.enabled
  • memory.embeddings_enabled
• In crates/openfang-kernel/src/kernel.rs:
  • skips embedding driver initialization when memory is disabled
  • skips embedding driver initialization when embeddings are disabled
  • passes the effective runtime flags into agent manifest metadata
• In crates/openfang-runtime/src/agent_loop.rs:
  • skips recall entirely when memory is disabled
  • disables embedding-backed recall when embeddings are disabled
  • skips remember / remember_with_embedding writes when memory is disabled
  • does this in both streaming and non-streaming loops

Why this is useful upstream

• It makes runtime behavior explicit and configurable.
• It reduces unwanted provider calls and noisy fallback behavior.
• It gives users a supported way to choose between full memory, text-only memory, and no memory.
• Defaults remain enabled, so existing behavior is preserved unless explicitly changed.

Validation

• cargo check -p openfang-runtime -p openfang-kernel -p openfang-types

[jaberjaber23]

Reviewed. The feature logic is correct but CI is failing (format check and ubuntu test). Please run cargo fmt and add unit tests for MemoryConfig defaults and deserialization with missing fields.