DRY/YAGNI/KISS pass: shared navigation registry, hide tracker, press gates

[ivanbanov]

A simplicity pass over the DOM layer and the dialog substrates, plus the principles it was held to written into AGENTS.md.

What changed

@dunky.dev/browser-navigation — fix. The guard registry and popstate listener now anchor on a realm-global keyed by Symbol.for, the same anchoring dom-overlay and dom-scroll-lock already use. Duplicate copies of the module (monorepo, micro-frontend) previously forked the registry while sharing the one real session history, so a Back could be answered by the wrong copy. The store also remembers the attached listener: each copy's function has its own identity, so the browser's (type, listener) dedupe can't span copies. Covered by an anchoring test mirroring the other two packages.

@dunky.dev/dom-dialog — press gates replace the predicates (minor). acceptsBackdropPress / acceptsViewportPress left React and Solid writing the same onClick wrapper by hand — exactly the shared DOM behavior this package exists to hold. gateBackdropPress(id, bindings) / gateViewportPress(id, bindings) take the part's normalized bindings and return them with the press gated; both substrates' Backdrop/Viewport collapse to a single mergeProps call. Gating rules unchanged.

@dunky.dev/dom-overlay + @dunky.dev/overlay — refactors, no behavior change. hideOutside and hideExitingLayer each carried a copy of the hide/undo bookkeeping (the author-hidden skip, the exact-restore undo); it's now one shared tracker so the two rules can't drift apart. In the layer stack, below(id) re-implemented the depth/open-order ranking; it now slices ordered() — one ranking rule, written once.

AGENTS.md. A Principles table (KISS, DRY, YAGNI, POLA) at the top of the Code section, so the lens this pass applied is the standing contract.

Also removed along the way: a stale dist-only leftover at packages/dom/utils/dialog/ (local, gitignored — nothing in the diff).

Not changed, deliberately

The forward-reopen half of closeOnBack is where the repo's complexity concentrates (parked guards, claim watchers, the consumption chain). Whether it earns its keep is a product decision, so this pass left it intact — flagged separately.

Verification

282 tests across 16 files, typecheck, and lint all pass. format:check still fails only on files this PR doesn't touch (pre-existing drift in README.md and the react/solid dialog SPECs).

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