Improve .describe() strings based on code review feedback

Co-authored-by: hotlong <50353452+hotlong@users.noreply.github.com>

Author: Copilot

packages/spec/src/cloud/marketplace.zod.ts

@@ -213,7 +213,7 @@ export const MarketplaceListingSchema = z.object({
 
   /** Current listing status */
   status: ListingStatusSchema.default('draft')
-    .describe('Current listing status'),
+    .describe('Publication state: draft, published, under-review, suspended, deprecated, or unlisted'),
 
   /** Display name */
   name: z.string().describe('Display name'),

packages/spec/src/kernel/package-registry.zod.ts

@@ -59,7 +59,7 @@ export const InstalledPackageSchema = z.object({
    * Current lifecycle status.
    */
   status: PackageStatusEnum.default('installed')
-    .describe('Current lifecycle status'),
+    .describe('Package state: installed, disabled, installing, upgrading, uninstalling, or error'),
 
   /**
    * Whether the package is currently enabled (active).

packages/spec/src/kernel/package-upgrade.zod.ts

@@ -54,7 +54,7 @@ export const MetadataDiffItemSchema = z.object({
   name: z.string().describe('Metadata name'),
 
   /** Type of change */
-  changeType: MetadataChangeTypeSchema.describe('Type of change'),
+  changeType: MetadataChangeTypeSchema.describe('Category of metadata modification (added, modified, removed, or renamed)'),
 
   /** Whether this change has potential conflicts with customizations */
   hasConflict: z.boolean().default(false)
@@ -95,7 +95,7 @@ export const UpgradePlanSchema = z.object({
   toVersion: z.string().describe('Target upgrade version'),
 
   /** Overall impact level */
-  impactLevel: UpgradeImpactLevelSchema.describe('Overall upgrade impact level'),
+  impactLevel: UpgradeImpactLevelSchema.describe('Severity assessment from none (seamless) to critical (breaking changes)'),
 
   /** List of all metadata changes between versions */
   changes: z.array(MetadataDiffItemSchema).describe('All metadata changes'),