feat(playground): add types.ts with static provider pricing table

Re-exports all playground types and adds static MODEL_PRICING_TABLE with
8-10 popular models labeled (estimated) for client-side cost estimation (D13).
Exports getModelPricing and getProviderPricing helpers.

src/lib/playground/types.ts

@@ -0,0 +1,114 @@
+// src/lib/playground/types.ts
+// Re-exports from codeExport + standalone pricing table
+
+export type {
+  PlaygroundEndpoint,
+  ExportLanguage,
+  ChatMessage,
+  ToolDefinition,
+  PlaygroundState,
+} from "./codeExport";
+
+export { PlaygroundStateSchema, API_KEY_PLACEHOLDER, exportCode, exportAllLanguages, endpointToPath } from "./codeExport";
+
+export type { ImprovePromptRequest, ImprovePromptResult } from "./promptImprover";
+
+export {
+  ImprovePromptRequestSchema,
+  META_SYSTEM_PROMPT,
+  buildImproveChatBody,
+  parseImprovedContent,
+} from "./promptImprover";
+
+/**
+ * Pricing entry for a model.
+ * Label "(estimated)" indicates these are approximate values for UI display (D13).
+ */
+export interface ProviderPricing {
+  /** Cost per 1k input tokens in USD. */
+  inUsdPer1k: number;
+  /** Cost per 1k output tokens in USD. */
+  outUsdPer1k: number;
+  /** Display label — always includes "(estimated)". */
+  label: string;
+}
+
+/**
+ * Static inline pricing table for popular models.
+ * Used in client-side cost estimation (D13).
+ * DO NOT use for billing — always labeled "(estimated)".
+ *
+ * Prices are approximate as of 2025. For real billing see /api/usage.
+ */
+export const MODEL_PRICING_TABLE: Record<string, ProviderPricing> = {
+  "gpt-4o": {
+    inUsdPer1k: 0.0025,
+    outUsdPer1k: 0.01,
+    label: "(estimated)",
+  },
+  "gpt-4o-mini": {
+    inUsdPer1k: 0.00015,
+    outUsdPer1k: 0.0006,
+    label: "(estimated)",
+  },
+  "claude-sonnet-4-6": {
+    inUsdPer1k: 0.003,
+    outUsdPer1k: 0.015,
+    label: "(estimated)",
+  },
+  "claude-opus-4-7": {
+    inUsdPer1k: 0.015,
+    outUsdPer1k: 0.075,
+    label: "(estimated)",
+  },
+  "claude-haiku-4-5": {
+    inUsdPer1k: 0.0008,
+    outUsdPer1k: 0.004,
+    label: "(estimated)",
+  },
+  "gemini-2.5-pro": {
+    inUsdPer1k: 0.00125,
+    outUsdPer1k: 0.01,
+    label: "(estimated)",
+  },
+  "gemini-2.0-flash": {
+    inUsdPer1k: 0.0001,
+    outUsdPer1k: 0.0004,
+    label: "(estimated)",
+  },
+  "deepseek-chat": {
+    inUsdPer1k: 0.00014,
+    outUsdPer1k: 0.00028,
+    label: "(estimated)",
+  },
+  "llama-3.3-70b": {
+    inUsdPer1k: 0.00059,
+    outUsdPer1k: 0.00079,
+    label: "(estimated)",
+  },
+  "mistral-large": {
+    inUsdPer1k: 0.002,
+    outUsdPer1k: 0.006,
+    label: "(estimated)",
+  },
+};
+
+/**
+ * Look up pricing for a model by name.
+ * Returns null if not found (use upstream usage data instead).
+ */
+export function getModelPricing(model: string): ProviderPricing | null {
+  return MODEL_PRICING_TABLE[model] ?? null;
+}
+
+/**
+ * Look up pricing for a model — alias with explicit `estimated: true` in return type.
+ * Required by §3 contract: `getProviderPricing(model): { inUsdPer1k, outUsdPer1k, estimated: true } | null`.
+ */
+export function getProviderPricing(
+  model: string,
+): { inUsdPer1k: number; outUsdPer1k: number; estimated: true } | null {
+  const entry = MODEL_PRICING_TABLE[model];
+  if (!entry) return null;
+  return { inUsdPer1k: entry.inUsdPer1k, outUsdPer1k: entry.outUsdPer1k, estimated: true };
+}