Remove upstream workflows not relevant to our fork

Keep only build.yml (Docker build + push to GHCR).
Removed: docker.yml, e2e.yml, pr.yml, refresh-lockfile.yml,
release.yml, release-smoke.yml.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.github/workflows/e2e.yml

@@ -1,44 +0,0 @@
-name: E2E Tests
-
-on:
-  workflow_dispatch:
-    inputs:
-      skip_llm:
-        description: "Skip LLM-dependent assertions (default: true)"
-        type: boolean
-        default: true
-
-jobs:
-  e2e:
-    runs-on: ubuntu-latest
-    timeout-minutes: 30
-    env:
-      PAPERCLIP_E2E_SKIP_LLM: ${{ inputs.skip_llm && 'true' || 'false' }}
-      ANTHROPIC_API_KEY: ${{ secrets.ANTHROPIC_API_KEY }}
-    steps:
-      - uses: actions/checkout@v4
-
-      - uses: pnpm/action-setup@v4
-        with:
-          version: 9
-
-      - uses: actions/setup-node@v4
-        with:
-          node-version: 20
-          cache: pnpm
-
-      - run: pnpm install --frozen-lockfile
-      - run: pnpm build
-      - run: npx playwright install --with-deps chromium
-
-      - name: Run e2e tests
-        run: pnpm run test:e2e
-
-      - uses: actions/upload-artifact@v4
-        if: always()
-        with:
-          name: playwright-report
-          path: |
-            tests/e2e/playwright-report/
-            tests/e2e/test-results/
-          retention-days: 14