Lazy-load EMF stylesheet

[elkimek]

What changed

• defer css/emf.css until the existing lazy EMF runtime opens the assessment UI
• preserve stylesheet cascade order, offline precaching, concurrent-load sharing, and cache-busted retry behavior
• contain stylesheet failures with a visible error instead of opening an unstyled editor
• add browser coverage for load caching, retry, failure containment, and the real EMF entry path
• ratchet the cold-load request and byte budgets and update architecture/audit documentation

Why

The EMF JavaScript feature was already lazy, but its feature-only stylesheet was still fetched on every returning-user startup. Loading both together removes that unnecessary cold-load request without changing EMF entry points or offline availability.

Impact

Measured on the same local cold mobile returning-user scenario:

• requests: 438 → 437
• compressed bytes: 1,846,079 → 1,844,244 (-1,835)
• decoded bytes: 5,585,960 → 5,577,570 (-8,390)

Validation

• COVERAGE=1 ./run-tests.sh
• 487 Vitest/Node tests passed
• 407 Chromium tests passed
• 472 responsive-theme assertions passed
• 67.29% combined function coverage passed the 67.10% ratchet
• type checks, architecture checks, vendor integrity, module verification, and cold-load budget passed