perf(ci): skip container init for changeset PRs (#2902)

* fix(ci): configure git remote with App token in release workflow

The changesets/action pushes commits using the default GITHUB_TOKEN
credential, which GitHub ignores for triggering downstream workflows.
This left the Version Packages PR (#2881) stuck with required checks
(ci, Cypress E2E, Create Agents E2E) permanently waiting.

Configures the git remote URL with the inkeep-internal-ci App token
before changesets/action runs — same pattern applied to ci.yml and
auto-format.yml in #2871.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* perf(ci): skip container init for changeset PRs by extracting check job

Service containers (Doltgres, Postgres) in cypress-e2e and
create-agents-e2e were initialized before the changeset check ran,
wasting ~30s of ubuntu-32gb runner time on every changeset PR.

Extracts the changeset check into a lightweight job on ubuntu-latest
that runs first. The heavy jobs now depend on it via `needs:` and
skip entirely (including container init) when it's a changeset PR.

Also removes all redundant step-level `if: changeset-check` guards
since the job-level `if` already gates everything.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refactor(ci): extract changeset check into reusable composite action

The changeset detection logic (~60 lines of shell) was duplicated
across ci.yml and cypress.yml. Extracts it into a shared composite
action at .github/composite-actions/changeset-check/action.yml.

Both workflows now do a sparse checkout (just the composite action
directory) and delegate to the shared action, keeping the changeset
detection logic in one place.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: amikofalvy

.github/composite-actions/changeset-check/action.yml

@@ -0,0 +1,68 @@
+name: "Changeset Check"
+description: "Detects changeset PRs (branch name, merge group, or changeset-only file changes) and outputs a skip flag"
+
+outputs:
+  is_changeset:
+    description: "Whether this is a changeset PR that should skip heavy CI jobs"
+    value: ${{ steps.check.outputs.is_changeset }}
+
+runs:
+  using: composite
+  steps:
+    - name: Check if changeset PR
+      id: check
+      shell: bash
+      run: |
+        IS_CHANGESET=false
+
+        # Pull request: check branch name directly
+        if [ "$HEAD_REF" = "changeset-release/main" ]; then
+          IS_CHANGESET=true
+          echo "Changeset PR detected via branch name"
+        fi
+
+        # Merge group: extract PR number from ref and check branch via API
+        if [ "$GITHUB_EVENT_NAME" = "merge_group" ] && [ "$IS_CHANGESET" = "false" ]; then
+          PR_NUM=$(echo "$MERGE_GROUP_HEAD_REF" | sed -n 's|.*/pr-\([0-9]*\)-.*|\1|p')
+          if [ -n "$PR_NUM" ]; then
+            BRANCH=$(gh pr view "$PR_NUM" --repo "$GITHUB_REPOSITORY" --json headRefName -q .headRefName 2>/dev/null || echo "")
+            if [ "$BRANCH" = "changeset-release/main" ]; then
+              IS_CHANGESET=true
+              echo "Changeset PR detected via merge group (PR #$PR_NUM)"
+            fi
+          fi
+        fi
+
+        # Check if PR only contains .changeset/ file changes
+        if [ "$IS_CHANGESET" = "false" ] && [ "$GITHUB_EVENT_NAME" != "push" ]; then
+          if [ "$GITHUB_EVENT_NAME" = "pull_request" ] && [ -n "$PR_NUMBER" ]; then
+            if ! CHANGED_FILES=$(gh pr diff "$PR_NUMBER" --name-only --repo "$GITHUB_REPOSITORY" 2>&1); then
+              echo "::warning::Failed to fetch PR diff for #$PR_NUMBER: $CHANGED_FILES"
+              CHANGED_FILES=""
+            fi
+          elif [ "$GITHUB_EVENT_NAME" = "merge_group" ] && [ -n "$PR_NUM" ]; then
+            if ! CHANGED_FILES=$(gh pr diff "$PR_NUM" --name-only --repo "$GITHUB_REPOSITORY" 2>&1); then
+              echo "::warning::Failed to fetch PR diff for #$PR_NUM: $CHANGED_FILES"
+              CHANGED_FILES=""
+            fi
+          fi
+
+          if [ -n "$CHANGED_FILES" ]; then
+            NON_CHANGESET=$(echo "$CHANGED_FILES" | grep -v '^\.changeset/' || true)
+            if [ -z "$NON_CHANGESET" ]; then
+              IS_CHANGESET=true
+              echo "Only .changeset/ files changed — skipping heavy CI jobs"
+            fi
+          fi
+        fi
+
+        echo "is_changeset=$IS_CHANGESET" >> $GITHUB_OUTPUT
+        if [ "$IS_CHANGESET" = "true" ]; then
+          echo "Changeset PR — skipping heavy CI jobs"
+        fi
+      env:
+        HEAD_REF: ${{ github.head_ref }}
+        GITHUB_EVENT_NAME: ${{ github.event_name }}
+        MERGE_GROUP_HEAD_REF: ${{ github.event.merge_group.head_ref }}
+        GH_TOKEN: ${{ github.token }}
+        PR_NUMBER: ${{ github.event.pull_request.number }}