feat: make McpbManifest a discriminated union of all versions

Changed McpbManifest type from a single version to a discriminated union
of all historical manifest versions (0.1, 0.2, 0.3).

This allows the type system to properly handle manifests from any version
while maintaining type safety through the manifest_version/dxt_version
discriminator field.

Benefits:
- Type-safe handling of multiple manifest versions
- TypeScript can narrow types based on version field
- No need for type assertions when working with versioned manifests
- Maintains backward compatibility with all historical versions

src/types.ts

@@ -15,6 +15,9 @@ import type {
   McpbUserConfigValuesSchema,
   McpServerConfigSchema,
 } from "./schemas/latest.js";
+import type { McpbManifestSchema as McpbManifestSchema_v0_1 } from "./schemas/0.1.js";
+import type { McpbManifestSchema as McpbManifestSchema_v0_2 } from "./schemas/0.2.js";
+import type { McpbManifestSchema as McpbManifestSchema_v0_3 } from "./schemas/0.3.js";
 
 export type McpServerConfig = z.infer<typeof McpServerConfigSchema>;
 
@@ -46,7 +49,14 @@ export type McpbUserConfigurationOption = z.infer<
 
 export type McpbUserConfigValues = z.infer<typeof McpbUserConfigValuesSchema>;
 
-export type McpbManifest = z.infer<typeof McpbManifestSchema>;
+/**
+ * Discriminated union of all supported manifest versions.
+ * Discriminated by manifest_version or dxt_version field.
+ */
+export type McpbManifest =
+  | z.infer<typeof McpbManifestSchema_v0_1>
+  | z.infer<typeof McpbManifestSchema_v0_2>
+  | z.infer<typeof McpbManifestSchema_v0_3>;
 
 /**
  * Information about a MCPB package signature