docs: update README with ergonomic type import improvements

Updated Type Safety section to show that commonly-used types are now
exported from the main adcp package, including:
- Core domain types (BrandManifest, Creative, MediaBuy, Package, etc.)
- Status enums (CreativeStatus, MediaBuyStatus, PackageStatus, PricingModel)
- All 9 pricing options with discriminators
- Request/Response types for all operations

Added examples showing type-safe pricing options and status enum usage.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: bokelley

README.md

@@ -207,10 +207,16 @@ client = ADCPClient(config)
 
 ### Type Safety
 
-Full type hints with Pydantic validation and auto-generated types from the AdCP spec:
+Full type hints with Pydantic validation and auto-generated types from the AdCP spec. All commonly-used types are exported from the main `adcp` package for convenience:
 
 ```python
-from adcp import GetProductsRequest
+from adcp import (
+    GetProductsRequest,
+    BrandManifest,
+    Package,
+    CpmFixedRatePricingOption,
+    MediaBuyStatus,
+)
 
 # All methods require typed request objects
 request = GetProductsRequest(brief="Coffee brands", max_results=10)
@@ -220,8 +226,27 @@ result = await agent.get_products(request)
 if result.success:
     for product in result.data.products:
         print(product.name, product.pricing_options)  # Full IDE autocomplete!
+
+# Type-safe pricing with discriminators
+pricing = CpmFixedRatePricingOption(
+    pricing_option_id="cpm_usd",
+    pricing_model="cpm",
+    is_fixed=True,  # Literal[True] - type checked!
+    currency="USD",
+    rate=5.0
+)
+
+# Type-safe status enums
+if media_buy.status == MediaBuyStatus.active:
+    print("Media buy is active")
 ```
 
+**Exported from main package:**
+- **Core domain types**: `BrandManifest`, `Creative`, `CreativeManifest`, `MediaBuy`, `Package`
+- **Status enums**: `CreativeStatus`, `MediaBuyStatus`, `PackageStatus`, `PricingModel`
+- **All 9 pricing options**: `CpcPricingOption`, `CpmFixedRatePricingOption`, `VcpmAuctionPricingOption`, etc.
+- **Request/Response types**: All 16 operations with full request/response types
+
 #### Semantic Type Aliases
 
 For discriminated union types (success/error responses), use semantic aliases for clearer code: