provider: Add EmberCloud integration

[tylersyin]

Add EmberCloud as a new provider to the gateway, enabling access to GLM and MiniMax AI models through EmberCloud's OpenAI-compatible API.

Supported models: glm-5, glm-4.7, glm-4.7-flash, glm-4.6, glm-4.5, glm-4.5-air, minimax-m2.5.

Description: (required)

• Add EmberCloud as a new provider to the gateway, enabling access to GLM and MiniMax AI models through EmberCloud's OpenAI-compatible API
  (https://api.embercloud.ai/v1)
• Supported models: glm-5, glm-4.7, glm-4.7-flash, glm-4.6, glm-4.5, glm-4.5-air, minimax-m2.5
• Implements standard OpenAI-compatible provider pattern (same as OVHCloud, Groq): api.ts for API config, chatComplete.ts for chat params and stream transforms,
  index.ts for provider config export
• Registers provider constant EMBER_CLOUD in globals.ts and adds to VALID_PROVIDERS
• Adds provider metadata entry in providers.json

Tests Run/Test cases added: (required)

• Ran npm run test:gateway — all 47 passing tests continue to pass; 8 pre-existing test suite failures (unrelated to this PR: broken mock paths, missing
  .creds.json, TS errors in bytez/api.ts)
• Build succeeds via rollup -c (verified through pre-push hook)
• Gateway starts successfully and is ready for connections at localhost:8787

Type of Change:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)