Read embedding settings from runtime config

[Dominic Nguyen (datduyng)]

Follow-up to #3096.

• embeddingProvider reads the embedding: section from the typed runtime config instead of process.env. The config package already parses these env vars, so values set by env, .env, or YAML still apply.
• The Copilot memory plugin rebuilds the runtime config after it removes copilot providers from env, so the removal still takes effect when the config is already cached.
• Config warns when a positive-integer setting (e.g. embedding.size) is invalid.
• getEmbeddingSize doc refers to the default-size constants.
• createEmbeddingModel logs model/batch-size overrides (typeagent:openai).
• KnowPro uses getEmbeddingSize() for caller-supplied models too, instead of a hardcoded 1536.