ci(repo): overlay HEAD's ui build wiring onto baseline worktree

snapi's baseline worktree checks out the PR's base branch but uses
HEAD's snapi config. When a watched package's build:declarations task
is added in the same PR that starts watching it, the baseline tree
doesn't yet have the task and the fallback build fails. Copy ui's
package.json and tsconfig.declarations.json from HEAD into the
worktree before installing, matching the existing pattern for
snapi.config.json.

Author: jacekradko

.github/workflows/api-changes.yml

@@ -131,6 +131,12 @@ jobs:
           mkdir -p .worktrees
           git worktree add .worktrees/snapi-baseline "origin/${GITHUB_BASE_REF}"
           cp snapi.config.json .worktrees/snapi-baseline/snapi.config.json
+          # Overlay HEAD's build:declarations wiring for watched packages onto
+          # the baseline. snapi watches a package set defined by HEAD, so the
+          # baseline must produce declarations the same way, even if a watched
+          # package only acquired its build:declarations task in this PR.
+          cp packages/ui/package.json .worktrees/snapi-baseline/packages/ui/package.json
+          cp packages/ui/tsconfig.declarations.json .worktrees/snapi-baseline/packages/ui/tsconfig.declarations.json
 
       - name: Install baseline dependencies
         if: steps.baseline-cache.outputs.cache-matched-key == ''