otel: normalize gen_ai.response.model to match request format

Anthropic responses echo the same logical model with a different separator
(e.g. request 'claude-opus-4.6' resolves to 'claude-opus-4-6'), causing
GROUP BY / DISTINCT on gen_ai.response.model to produce duplicate rows.

Add normalizeResponseModel(requestModel, responseModel) that echoes the
request value when the two strings only differ in '.' vs '-', and returns
the resolved value unchanged when it adds real specificity (e.g.
'gpt-5.4-mini' -> 'gpt-5.4-mini-2026-03-17'). Wire into the three call
sites that set gen_ai.response.model: chatMLFetcher (chat spans),
toolCallingLoop (foreground invoke_agent), and claudeOTelTracker
(Claude invoke_agent).

Fixes #318805