feat(providers): add grok-cli and kimi-coding to CONNECTION_BILLING_CATALOG

Problem / Use Case

OmniRoute's filterSubscriptionOnlyCandidates() in the auto-routing pipeline validates candidates against CONNECTION_BILLING_CATALOG via classifyConnectionBilling(). Currently, only claude, codex, antigravity, cursor, copilot-web, and devin-desktop are curated in that catalog.

When operators authenticate with grok-cli (OAuth / Grok subscription) or kimi-coding (OAuth), OmniRoute defaults their billing classification to unknown / metered. Consequently, structured auto routes enforcing zero marginal token cost (such as auto/<category>:subscription) completely filter out Grok and Kimi, even when their OAuth quota is active and healthy.

Proposed Solution

Add entries to CONNECTION_BILLING_CATALOG in open-sse/services/routing/billingCatalog.ts (or corresponding module):

{
  provider: "grok-cli",
  authType: "oauth",
  billing: "subscription",
  overage: "hard-stop",
  reason: "Grok CLI OAuth serves the operator's Grok subscription tier quota. Exhaustion is refused until the plan window resets rather than billed."
},
{
  provider: "kimi-coding",
  authType: "oauth",
  billing: "subscription",
  overage: "hard-stop",
  reason: "Kimi Coding OAuth serves the operator's included plan quota with hard-stop overage."
}

Additionally, consider allowing operators to declare custom subscription providers via an environment variable or config setting (e.g. OMNIROUTE_SUBSCRIPTION_PROVIDERS=grok-cli,kimi-coding) so newly supported OAuth providers do not require waiting on upstream catalog updates.

Acceptance Criteria

• grok-cli OAuth connections evaluate to billing: 'subscription' and overage: 'hard-stop'.
• kimi-coding OAuth connections evaluate to billing: 'subscription' and overage: 'hard-stop'.
• Requests to auto/*:subscription admit healthy grok-cli and kimi-coding connections into the candidate pool.

Area

• Proxy / Routing
• Provider Support
• OAuth / Authentication