feat(costs): add agent model breakdown, harden date validation, sync CostByProject type, fix quota threshold and tab-gated queries

- add byAgentModel endpoint and expandable per-agent model sub-rows in the spend tab
- validate date range inputs with isNaN + badRequest to return HTTP 400 on bad input
- move CostByProject from a local api/costs.ts definition into packages/shared types
- gate providerData query on mainTab === providers, consistent with weekData/windowData/quotaData
- fix byProject range filter from finishedAt to startedAt, consistent with byProvider runs query
- fix WHAM used_percent threshold from <= 1 to < 1 to avoid misclassifying 1% usage as 100%
- replace inline opacity style with tailwind bg-primary/85 class in ProviderQuotaCard
- reset expandedAgents set when company or date range changes
- sort agent model sub-rows by cost descending in ui memo

packages/shared/src/index.ts

@@ -133,7 +133,9 @@ export type {
   CostSummary,
   CostByAgent,
   CostByProviderModel,
+  CostByAgentModel,
   CostWindowSpendRow,
+  CostByProject,
   HeartbeatRun,
   HeartbeatRunEvent,
   AgentRuntimeState,