feat(ai-chat): add direct Meta API provider integration

[dileep812]

Fixes #3519

Description

Adds direct Meta API integration to Puter's AI Chat Driver, enabling native execution of Meta models (meta:muse-spark-1.2, meta:muse-spark-1.1, and meta:muse-code-1.0) alongside existing providers.

Changes

1. models.ts: Defined META_MODELS with context limits (1,048,576 tokens), max output caps (8,192 tokens), cost keys (prompt_tokens, completion_tokens), and alias mappings.
2. MetaProvider.ts: Implemented IChatProvider interface using OpenAI SDK compatibility pointing to Meta's API endpoint (https://api.meta.ai/v1). Configured accurate token usage cost calculations in usage_calculator.
3. ChatCompletionDriver.ts: Wired MetaProvider into ChatCompletionDriver provider map when providers['meta'] key is configured.
4. config.template.jsonc: Added "meta" configuration block under "ai".
5. MetaProvider.test.ts: Added unit test suite covering initialization, catalog methods, model listing, completion output, and cost override calculation assertions.

How Has This Been Tested?

Ran backend Vitest suite:

npm run test:backend -- MetaProvider.test.ts ChatCompletionDriver.test.ts