Integrate CodexKit products into CodexReviewKit

[lynnswap]

Purpose

Move the Codex app-server and data products into CodexReviewKit so the SDK and its primary consumer share one repository, one package graph, and one revision. This removes the remote-pin/local-override split that allowed Xcode and SwiftPM to compile different CodexKit checkouts.

Changes

• Import CodexAppServerKit, CodexAppServerKitTesting, and CodexDataKit from CodexKit commit ab025ed970d30c7679913951bdb9fff20a9b77b1.
• Preserve the three product names, module names, and public API surface while raising the unified package deployment target to macOS 26.
• Remove one unused package-only enqueueAccount overload that became ambiguous after the targets moved into the same package; the public overload remains unchanged.
• Replace CodexKit package edges with same-package target dependencies and remove the old remote pin and local-override discovery.
• Link the Review Monitor app directly to the root package's CodexDataKit product.
• Add a standalone consumer fixture that imports, links, and runs all three migrated products.
• Add dedicated CI shards for the imported AppServerKit and DataKit test suites, plus the external consumer contract.
• Document the target ownership, migration contract, and post-merge CodexKit archival sequence.

Consumer migration

Consumers should change their Swift package URL and package identity from CodexKit to CodexReviewKit. Existing imports and product names remain unchanged:

• CodexAppServerKit
• CodexAppServerKitTesting
• CodexDataKit

The standalone CodexKit repository can remain pinned at its final commit for older macOS deployments. It will be marked as moved and archived only after this integration lands.

Validation

• swift test --build-system swiftbuild --no-parallel
• swift test --build-system swiftbuild --no-parallel --test-product CodexAppServerKitTests (405 tests)
• swift test --build-system swiftbuild --no-parallel --test-product CodexDataKitTests (346 tests)
• swift run --package-path Fixtures/CodexReviewKitProductConsumer
• xcodebuild test -project Tools/ReviewMonitor/CodexReviewMonitor.xcodeproj -scheme CodexReviewMonitor -destination 'platform=macOS,arch=arm64' CODE_SIGNING_ALLOWED=NO CODE_SIGNING_REQUIRED=NO
• actionlint
• ruby scripts/verify-github-actions-pinning.rb
• git diff --check origin/main...HEAD
• Codex self-review against main: 0 findings

No screenshots are needed because this PR changes package ownership and build wiring without changing the rendered UI.