perf: trim page export bundles and issue count annotations

[d0cd]

Summary

• replace repeated per-issue count subqueries with shared aggregate annotations for links, attachments, and sub-issues
• add a focused test covering the shared issue count annotation helper
• move page export PDF styles and runtime imports behind lazy boundaries so @react-pdf/renderer is no longer loaded in the always-on page header path

Verification

• pnpm --filter=web build
• /tmp/plane-api-venv/bin/python -m compileall apps/api/plane/app/views/issue/base.py apps/api/plane/tests/unit/views/test_issue_counts.py

Notes

• Live API/browser profiling was limited by unstable local infra containers, so I used deterministic build output and server-side query inspection for this pass.

🌒 Run on Niteshift: View Task