Improve file organization to reduce cycles

Checking the real runtime graph, there are exactly two cycles:

1. cascade → utils → dom → cascade (with utils ↔ dom nested inside it)

This is the one that actually bites. Probing module-body evaluation shows SHIFTED_PROPERTIES is not yet initialized when dom.ts's body runs — it only gets away with it because the read happens inside getCSSPropertyValue rather than at module scope. All three edges are single-use:

• dom → cascade exists solely for SHIFTED_PROPERTIES (dom.ts:51)

• utils → dom exists solely for strategyForElement (utils.ts:292 → getCSSPropertyValue)

• dom → utils exists solely for getRootStyleContainer (dom.ts:105)

2. parse ↔ fallback

Only isIdentifier is a real value edge — AnchorPosition, AnchorPositions and TryBlock are types and already erase. parse needs parsePositionFallbacks; fallback needs those four.

Perhaps look at improving this in a new PR?

Originally posted by @jpzwarte in #448

Start by reading the runtime imports and module bodies in dom.ts, utils.ts, cascade, parse, and fallback, focusing on the edges and symbols identified in the issue. Confirm the two cycles and their evaluation behavior, then reorganize the modules so the cycles are removed without changing the affected behavior. Done means the listed runtime cycles no longer exist and module initialization remains safe.