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.
• Config warns when a positive-integer setting (e.g. embedding.size) is invalid, instead of ignoring it silently.
• getEmbeddingSize doc refers to the default-size constants, so it cannot drift.
• createEmbeddingModel logs model/batch-size overrides of the pool settings (typeagent:openai).
• KnowPro uses getEmbeddingSize() for caller-supplied models too, instead of a hardcoded 1536.

[robgruen]

Looks great, thanks!