fix(sentiment): stripCodeFences before JSON.parse (closes #296)

[iPLAYCAFE-dev]

Closes #296.

analyzeSentiment in sentiment.service.ts does a bare JSON.parse on the chat response, unlike summary.service.ts:146 and merge-assessment.service.ts which both wrap it in stripCodeFences(...). Any provider/model that wraps the json_object output in ```json ... ``` fences — even with response_format: { type: 'json_object' } — therefore throws JSON Parse error: Unrecognized token ''` and sentiment is dropped.

Verified live via OpenRouter: anthropic/claude-haiku-4.5 and deepseek/deepseek-chat fence the output; OpenAI models, claude-sonnet-4.6, google/gemini-3.1-flash-lite, and meta-llama/llama-3.3-70b-instruct return clean JSON.

This is the minimal fix: import the existing stripCodeFences helper and apply it before JSON.parse, exactly as the sibling summary/merge services already do. One-line behavior change, no new dependency.

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