ci(apple): add Xcode Cloud post-clone script

Xcode Cloud only checks out the repo, so ci_post_clone.sh installs swiftlint,
xcodegen and bun, downloads the prebuilt core (vnidrop.xcframework + Vnidrop.swift)
from the matching GitHub Release asset, and generates the project via localization,
version/app config codegen and xcodegen. Rust is never built on Xcode Cloud.

ci_scripts/README.md

@@ -0,0 +1,40 @@
+# Xcode Cloud CI scripts
+
+Xcode Cloud runs the scripts in this directory around each build. Only
+`ci_post_clone.sh` is used today; add `ci_pre_xcodebuild.sh` /
+`ci_post_xcodebuild.sh` here if later steps are needed.
+
+## What `ci_post_clone.sh` does
+
+The Xcode project (`apple/VniDrop.xcodeproj`) and its generated inputs are **not**
+committed — they are produced by XcodeGen, localization, and the Rust core build.
+Since Xcode Cloud only checks out the repository, the post-clone script:
+
+1. installs `swiftlint`, `xcodegen`, and `bun`;
+2. **downloads the prebuilt core** (`vnidrop.xcframework` + `Vnidrop.swift`) from
+   the matching GitHub Release asset `VnidropCore-<version>.zip` — Xcode Cloud
+   never builds Rust;
+3. runs localization + version/app config codegen and `xcodegen generate`
+   (equivalent to `make apple-project` without the `apple-core` step).
+
+The core asset for version `X.Y.Z` must be published on the `vX.Y.Z` release
+before an Xcode Cloud build for that version runs (see
+`apple/scripts/package-core.sh` and `.github/workflows/apple-release.yml`).
+
+### Overrides (env vars, optional)
+
+| Variable | Default | Purpose |
+|----------|---------|---------|
+| `VNIDROP_CORE_REPO` | `sudosylabs/vnidrop` | Release repository to download the core from |
+| `VNIDROP_CORE_TAG`  | `v<product-version>` | Release tag holding the core asset |
+
+## Workflow configuration (App Store Connect)
+
+The workflow itself (product, scheme, triggers, actions) is configured in App
+Store Connect, not in the repository. Point it at:
+
+- **Project:** `apple/VniDrop.xcodeproj` (generated by the post-clone script)
+- **Scheme:** `VniDrop` (App Store / TestFlight target; shared, see `apple/project.yml`)
+
+Archive actions use the release Rust profile via the published core asset; build
+and test actions reuse the same prebuilt core.