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

## New files
- btc-oracle.ts: CoinGecko BTC/USD fetch (60s cache), usdToSats() helper (ceil, min 1 sat),
  5s abort timeout, fallback to BTC_PRICE_USD_FALLBACK env var (default $100k)
- lib/db/migrations/0002_cost_based_pricing.sql: SQL migration artifact adding 6 new columns
  to jobs table (estimated_cost_usd, margin_pct, btc_price_usd, actual_input_tokens,
  actual_output_tokens, actual_cost_usd); idempotent via ADD COLUMN IF NOT EXISTS

## Modified files
- pricing.ts: Full rewrite — per-model token rates (Haiku/Sonnet, env-var overridable),
  DO infra amortisation per request, originator margin %, estimateInputTokens/Output by 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
- lib/db/src/schema/jobs.ts: 6 new real/integer columns; schema pushed to DB
- jobs.ts route: Work invoice creation calls pricingService.calculateWorkFeeSats() async;
  stores estimatedCostUsd/marginPct/btcPriceUsd; post-work stores actualInputTokens/
  actualOutputTokens/actualCostUsd; GET response includes pricingBreakdown and costLedger
  with totalTokens (input + output computed field)
- openapi.yaml: PricingBreakdown + CostLedger schemas (with totalTokens) added
- lib/api-zod/src/generated/api.ts: Regenerated with new schemas
- lib/api-client-react/src/generated/api.schemas.ts: Regenerated (PricingBreakdown, CostLedger)
- replit.md: 17 new env vars documented in cost-based pricing section

lib/api-zod/src/generated/api.ts

@@ -21,7 +21,7 @@ export const HealthCheckResponse = zod.object({
  */
 
 export const CreateJobBody = zod.object({
-  request: zod.string().min(1).max(500),
+  request: zod.string().min(1),
 });
 
 /**
@@ -55,8 +55,47 @@ export const GetJobResponse = zod.object({
       amountSats: zod.number(),
     })
     .optional(),
+  pricingBreakdown: zod
+    .object({
+      estimatedCostUsd: zod
+        .number()
+        .optional()
+        .describe(
+          "Total estimated cost in USD (token cost + DO infra + margin)",
+        ),
+      marginPct: zod
+        .number()
+        .optional()
+        .describe("Originator margin percentage applied"),
+      btcPriceUsd: zod
+        .number()
+        .optional()
+        .describe("BTC\/USD spot price used to convert the invoice to sats"),
+    })
+    .optional()
+    .describe(
+      "Cost breakdown shown with the work invoice (estimations at invoice-creation time)",
+    ),
   reason: zod.string().optional(),
   result: zod.string().optional(),
+  costLedger: zod
+    .object({
+      actualInputTokens: zod.number().optional(),
+      actualOutputTokens: zod.number().optional(),
+      totalTokens: zod
+        .number()
+        .optional()
+        .describe("Sum of actualInputTokens + actualOutputTokens"),
+      actualCostUsd: zod
+        .number()
+        .optional()
+        .describe("Raw Anthropic token cost (no infra, no margin)"),
+      estimatedCostUsd: zod.number().optional(),
+      marginPct: zod.number().optional(),
+      btcPriceUsd: zod.number().optional(),
+    })
+    .optional()
+    .describe("Actual cost record stored after the job completes"),
   errorMessage: zod.string().optional(),
 });
 
@@ -65,7 +104,7 @@ export const GetJobResponse = zod.object({
  * @summary Free demo (rate-limited)
  */
 export const RunDemoQueryParams = zod.object({
-  request: zod.string().min(1).max(500),
+  request: zod.coerce.string(),
 });
 
 export const RunDemoResponse = zod.object({