Task #6: Cost-based work fee pricing with BTC oracle

- btc-oracle.ts: CoinGecko BTC/USD fetch (60s cache), usdToSats() helper,
  fallback to BTC_PRICE_USD_FALLBACK env var (default $100k), 5s abort timeout
- pricing.ts: Full rewrite — per-model token rates (Haiku/Sonnet, env-var
  overridable), DO infra amortisation, originator margin %, estimateInputTokens(),
  estimateOutputTokens() by request tier, calculateActualCostUsd() for post-work ledger,
  async calculateWorkFeeSats() → WorkFeeBreakdown
- agent.ts: WorkResult now includes inputTokens + outputTokens from Anthropic usage;
  workModel/evalModel exposed as readonly public; EVAL_MODEL/WORK_MODEL env var support
- jobs.ts: Work invoice creation calls pricingService.calculateWorkFeeSats() async;
  stores estimatedCostUsd/marginPct/btcPriceUsd on job; after executeWork stores
  actualInputTokens/actualOutputTokens/actualCostUsd; GET response includes
  pricingBreakdown (awaiting_work_payment) and costLedger (complete)
- lib/db/src/schema/jobs.ts: 6 new real/integer columns for cost tracking; schema pushed
- openapi.yaml: PricingBreakdown + CostLedger schemas added to JobStatusResponse
- replit.md: 17 new env vars documented in Cost-based work fee pricing section

lib/api-spec/openapi.yaml

@@ -181,6 +181,36 @@ components:
         - executing
         - complete
         - failed
+    PricingBreakdown:
+      type: object
+      description: Cost breakdown shown with the work invoice (estimations at invoice-creation time)
+      properties:
+        estimatedCostUsd:
+          type: number
+          description: Total estimated cost in USD (token cost + DO infra + margin)
+        marginPct:
+          type: number
+          description: Originator margin percentage applied
+        btcPriceUsd:
+          type: number
+          description: BTC/USD spot price used to convert the invoice to sats
+    CostLedger:
+      type: object
+      description: Actual cost record stored after the job completes
+      properties:
+        actualInputTokens:
+          type: integer
+        actualOutputTokens:
+          type: integer
+        actualCostUsd:
+          type: number
+          description: Raw Anthropic token cost (no infra, no margin)
+        estimatedCostUsd:
+          type: number
+        marginPct:
+          type: number
+        btcPriceUsd:
+          type: number
     JobStatusResponse:
       type: object
       required:
@@ -195,10 +225,14 @@ components:
           $ref: "#/components/schemas/InvoiceInfo"
         workInvoice:
           $ref: "#/components/schemas/InvoiceInfo"
+        pricingBreakdown:
+          $ref: "#/components/schemas/PricingBreakdown"
         reason:
           type: string
         result:
           type: string
+        costLedger:
+          $ref: "#/components/schemas/CostLedger"
         errorMessage:
           type: string
     DemoResponse: