refactor(metadata): drop the dead @objectstack/platform-objects dependency

The retired `adr-0030-notification-event` migration runner was the only consumer.
Nothing under `packages/metadata/src` carries a `@objectstack/platform-objects`
specifier any more, so the manifest declared an edge the package no longer has.

Removed together, because all three exist only to serve that one dead edge:
  - `package.json`  — the `dependencies` entry
  - `vitest.config.ts` — the `@objectstack/platform-objects/system` alias, whose
    own comment cited the retired migration's receipt cases as its reason
  - `tsconfig.json` — the matching `paths` mapping

`pnpm-lock.yaml` travels in this commit, regenerated with `pnpm install
--lockfile-only` rather than hand-edited. Its entire diff is the three lines of
the one removed edge under the `packages/metadata` importer; a manifest edit
without it fails `ERR_PNPM_OUTDATED_LOCKFILE` at every job's install step.

Dropping a published package's dependency is a public-surface change, so it was
established rather than assumed that nothing resolves it through this package:

  - `@objectstack/metadata`'s built `dist/` (30 files, 10 declaration files)
    contains ZERO occurrences of `platform-objects`, against a positive control
    in which all nine other declared dependencies appear in 4-12 dist files
    each. No runtime import and no type reference reaches it.
  - Of the 23 workspace packages carrying a real `@objectstack/platform-objects`
    module specifier, all 23 declare it themselves; zero resolve it
    transitively. `check:undeclared-dep-imports` is the standing gate that keeps
    that true for non-test `src/**`.
  - Zero example apps reference it at all.

`@objectstack/platform-objects` publishes on its own, so a consumer that wants
it declares it directly — the supported spelling, unchanged.

Claude-Session: https://claude.ai/code/session_01DvvamiacK328idtBYJBxV3
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude

.changeset/17281-metadata-drops-dead-platform-objects-dep.md

@@ -0,0 +1,39 @@
+---
+'@objectstack/metadata': patch
+---
+
+`@objectstack/metadata` no longer declares `@objectstack/platform-objects`.
+
+The dependency was the retired `adr-0030-notification-event` migration runner's,
+and that runner was its only consumer. Nothing under `packages/metadata/src`
+carries a `@objectstack/platform-objects` specifier any more, so the declaration
+described an edge the package no longer has. The two test-tooling entries that
+existed only to serve it go with it: the `@objectstack/platform-objects/system`
+alias in `vitest.config.ts` (whose comment still cited the retired migration's
+receipt cases as its reason) and the matching `paths` mapping in `tsconfig.json`.
+
+## What an installing consumer should check
+
+⚠️ This is a **published** package dropping a declared dependency, so it changes
+what an install tree contains, not just what this repo builds. If you import
+`@objectstack/platform-objects` **without declaring it**, and it resolved for you
+only because `@objectstack/metadata` hoisted it, that resolution is gone — the
+fix is one line, and it is the supported spelling either way:
+
+```
+pnpm add @objectstack/platform-objects     # or npm/yarn equivalent
+```
+
+`@objectstack/platform-objects` is published on its own and is unchanged by this;
+nothing is renamed, removed or re-exported.
+
+⛔ Nothing `@objectstack/metadata` itself ships is affected. Measured rather than
+asserted: its built `dist/` (30 files, 10 declaration files) carries **zero**
+occurrences of `platform-objects`, against a positive control in which all nine
+of its other declared dependencies appear in four to twelve dist files each. No
+runtime import and no type reference reaches it, so no consumer can arrive at it
+through anything this package publishes.
+
+Grade `patch`, measured rather than defaulted: no export moves, no accept-set
+widens, no runtime behaviour changes. Not `skip-changeset` either — `package.json`
+is shipped by `npm pack`, and a consumer's install tree is what changes.

packages/metadata/package.json

@@ -83,7 +83,6 @@
     "@objectstack/core": "workspace:*",
     "@objectstack/metadata-core": "workspace:*",
     "@objectstack/metadata-fs": "workspace:*",
-    "@objectstack/platform-objects": "workspace:*",
     "@objectstack/spec": "workspace:*",
     "@objectstack/types": "workspace:*",
     "chokidar": "^5.0.0",

packages/metadata/tsconfig.json

@@ -13,9 +13,6 @@
     "types": [
       "node",
       "js-yaml"
-    ],
-    "paths": {
-      "@objectstack/platform-objects/system": ["../platform-objects/src/system/index.ts"]
-    }
+    ]
   }
 }

packages/metadata/vitest.config.ts

@@ -43,18 +43,6 @@ export default defineConfig({
         replacement: path.join(path.resolve(__dirname, '..'), 'spec/src/$1/index.ts'),
       },
       { find: /^@objectstack\/spec$/, replacement: path.resolve(__dirname, '../spec/src/index.ts') },
-      // [#16100] The deployment-ledger writer/reader pair the notification-event
-      // migration's receipt cases drive (`attestFreshDatastore` seeds the
-      // fresh-store row, `isDataMigrationVerified` reads the verdict back). The
-      // entry is ANCHORED on the subpath rather than spelled bare: this package
-      // publishes a FILE-shaped subpath (`./plugin`), so a bare prefix rule with
-      // a file replacement would resolve `…/system` to
-      // `…/platform-objects/src/index.ts/system` — ENOTDIR at run time, from a
-      // config that reads as correct.
-      {
-        find: /^@objectstack\/platform-objects\/system$/,
-        replacement: path.resolve(__dirname, '../platform-objects/src/system/index.ts'),
-      },
       // Subpath BEFORE the bare package, same prefix-match reason: `./node` is a
       // published subpath served by a FILE (`types/src/node.ts` — the node-only slice
       // the root export deliberately excludes), so the bare entry would resolve it to