feat: add billing/inferenceLog/agentChat module loaders + wire into agentic-server

[pyramation]

Summary

Adds three module loaders to express-context and wires them into agentic-server, replacing the package's internal discovery queries with the shared useModule() pattern.

express-context loaders added:

• billing — resolves BillingConfig (public/private schema, record_usage, check_billing_quota functions) from metaschema_modules_public.billing_module
• inferenceLog — resolves InferenceLogConfig (schema, table name) from metaschema_modules_public.inference_log_module
• agentChat — resolves AgentChatConfig (thread/message/task table names) from metaschema_modules_public.agent_chat_module

All three are registered in createDefaultRegistry() and exported from the package index. BuiltinModuleMap is updated for type-safe useModule() calls.

agentic-server changes:

• Router now uses ctx.useModule('agentChat') instead of getAgentDiscovery(ctx.pool, ctx.api.dbname)
• Router now uses ctx.useModule('billing') + ctx.useModule('inferenceLog') instead of getDatabaseConfig(ctx.pool, ctx.databaseId)
• billing.ts imports types from @constructive-io/express-context instead of local ./discovery
• The discovery.ts module remains exported as public API (backwards compat) but is no longer used internally by the router

Tests:

• Router tests rewritten to mock useModule instead of pool.query for discovery
• Added supertest + @types/supertest for proper HTTP assertions
• All 22 tests pass

Review & Testing Checklist for Human

• Verify the SQL queries in the three loaders match the actual metaschema_modules_public table schemas (billing_module, inference_log_module, agent_chat_module)
• Confirm the checkBillingQuotaFunction hardcoded value 'check_billing_quota' is correct for all deployments (or should come from the module row)
• Test with a real provisioned database that the loaders resolve correctly via req.constructive.useModule('billing') etc.

Notes

• The discovery.ts module in agentic-server is still exported but no longer used internally. It can be deprecated/removed in a follow-up.
• TTL values: billing (5 min), inferenceLog (5 min), agentChat (1 min) — matching the existing loader patterns.

Link to Devin session: https://app.devin.ai/sessions/2b5a29d83d3f478e8d3d972653b4879c
Requested by: @pyramation

[devin-ai-integration]

🤖 Devin AI Engineer

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR. Add '(aside)' to your comment to have me ignore it.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment and CI monitoring