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fix(print): patch pdfkit nextTick to use queueMicrotask instead of setTimeout(0)

Fix the Firefox worker hang at its true source instead of working around it.

pdfkit's browser build drives all of its async work - zlib for object and image
compression, and readable-stream completion ('data'/'end') - through its bundled
process/browser nextTick polyfill, which schedules via setTimeout(fun, 0). Under
heavy load (a Firefox web worker on a busy CI host) those setTimeout(0) callbacks
starve, so the final deflate/flush callbacks never run, 'end' never fires and
toBlob() hangs forever. Disabling compression only removed the object-compression
part; image zlib and stream completion still stalled, so the flake persisted.

Patch runTimeout() to schedule via queueMicrotask instead. Microtasks run at the
end of the current microtask checkpoint and never starve behind macrotask/CPU
load, which matches Node's process.nextTick semantics more closely. This drains
the whole pipeline promptly regardless of load.

With the scheduler fixed, revert the app-side workaround: toBlob() goes back to
the simple 'data'/'end' drain and the sync-drain helper/test are removed.
compress=false is kept for now and will be revisited once CI confirms this holds.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KQ8DeKNRbyq2fLVAqdJfof

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