fix: remove plugin versions from marketplace.json and fix brittle test

- Remove plugin version fields from marketplace.json -- canonical
  versions live in each plugin's plugin.json. Duplicating them created
  drift that release-please couldn't maintain.
- Remove version sync logic from metadata.ts (description sync kept)
- Fix release-preview test to compute expected versions dynamically
  from current manifests instead of hardcoding them

tests/release-preview.test.ts

@@ -1,8 +1,9 @@
 import { describe, expect, test } from "bun:test"
-import { buildReleasePreview } from "../src/release/components"
+import { buildReleasePreview, bumpVersion, loadCurrentVersions } from "../src/release/components"
 
 describe("release preview", () => {
   test("uses changed files to determine affected components and next versions", async () => {
+    const versions = await loadCurrentVersions()
     const preview = await buildReleasePreview({
       title: "fix: adjust ce:plan-beta wording",
       files: ["plugins/compound-engineering/skills/ce-plan-beta/SKILL.md"],
@@ -11,10 +12,11 @@ describe("release preview", () => {
     expect(preview.components).toHaveLength(1)
     expect(preview.components[0].component).toBe("compound-engineering")
     expect(preview.components[0].inferredBump).toBe("patch")
-    expect(preview.components[0].nextVersion).toBe("2.42.1")
+    expect(preview.components[0].nextVersion).toBe(bumpVersion(versions["compound-engineering"], "patch"))
   })
 
   test("supports per-component overrides without affecting unrelated components", async () => {
+    const versions = await loadCurrentVersions()
     const preview = await buildReleasePreview({
       title: "fix: update coding tutor prompts",
       files: ["plugins/coding-tutor/README.md"],
@@ -27,7 +29,7 @@ describe("release preview", () => {
     expect(preview.components[0].component).toBe("coding-tutor")
     expect(preview.components[0].inferredBump).toBe("patch")
     expect(preview.components[0].effectiveBump).toBe("minor")
-    expect(preview.components[0].nextVersion).toBe("1.3.0")
+    expect(preview.components[0].nextVersion).toBe(bumpVersion(versions["coding-tutor"], "minor"))
   })
 
   test("docs-only changes remain non-releasable by default", async () => {