feat: add fallback for models without tool calling support

[devin-ai-integration]

Summary

Fixes an issue where users get an error saying "tool calling not supported" when using models like Gemma via LM Studio for summarization.

The root cause: when no template is selected, generateTemplateIfNeeded uses the Vercel AI SDK's Output.object({ schema }) to generate template sections. This internally uses tool calling, which models like Gemma don't support.

Solution: Added a generateStructuredOutput helper that:

1. First attempts structured output via tool calling (for models that support it)
2. On failure, falls back to plain text generation with JSON extraction using regex
3. Validates the parsed JSON against the Zod schema

Review & Testing Checklist for Human

• Test with a model that doesn't support tool calling (e.g., Gemma via LM Studio) - verify summarization works without errors
• Test with a model that does support tool calling (e.g., GPT-4, Claude) - verify existing behavior is unchanged
• Review the regex pattern /\{[\s\S]*\}/ for JSON extraction - could it incorrectly match nested objects or fail on edge cases?
• Verify the fallback gracefully returns null (same as original behavior) when both approaches fail

Recommended test plan:

1. Set up LM Studio with Gemma model
2. Create a session with transcript content but no template selected
3. Trigger summarization and verify it completes without "tool calling not supported" error

Notes

• The error variable on line 206 is intentionally unused - it's caught to trigger the fallback
• Both primary and fallback paths return null on failure, maintaining the original graceful degradation behavior

Link to Devin run: https://app.devin.ai/sessions/9cc7c5ed1c564bb5b24bb602f3391179
Requested by: @ComputelessComputer

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[devin-ai-integration]

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