docs(ethereal): mark the CONTINUE hand-off body as historical

The top blocks already say FINALIZED, but the body still read as a live P1→P4
plan ("flag OFF", "runtime still @floating-ui", "P4 pending") — stale and
contradictory now that the finalize + flip rollout shipped. Replace the old
"Status: P1 COMPLETE" block with a clear HISTORICAL marker so the remaining plan
reads as the completed build record, not a to-do. Own engine is the runtime;
@floating-ui is out of the library; native path + avoidCollisions:'flip' shipped.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/uix/soma/layers/floating/CONTINUE.md

@@ -46,15 +46,14 @@
 > config. The paths below that say `engine/…` now mean `$ethereal/…`. **`@floating-ui`
 > is UNTOUCHED — P4 NOT executed** (dep installed, fui imports + flag intact, flag OFF).
 >
-> **Status: P1 COMPLETE — flag-gated, math-verified.** The whole engine is built
-> and compiling: DOM-read + clipping ancestor-walk + `detectOverflow` + all 7
-> middleware + `compute` (read phase + pure `runMiddleware` loop) + `autoUpdate` +
-> the `Middleware` de-vendor + the `USE_OWN_ENGINE` flag wiring. A 13-case parity
-> test (`engine/engine.test.ts`) proves the engine is **pixel-identical to
-> `@floating-ui`** on synthetic rects. The flag is **OFF by default** (runtime
-> still `@floating-ui`); flip `engine/flag.ts` to A/B in a browser. What remains
-> is broad foreground-browser A/B across every overlay (P2/P3) then the actual
-> `@floating-ui` deletion (P4). Branch: `alpha-0.1-sec-dom`. Read this cold to resume.
+> **⏳ HISTORICAL — the P1→P4 hand-off below is COMPLETE.** Everything from here
+> down is the original build/resume plan; its claims ("flag OFF", "runtime still
+> `@floating-ui`", "P4 pending", "the exact removal surface") describe the
+> PRE-FINALIZE state and are kept only as the build record. The current, true state
+> is the two blocks at the very top (FINALIZED + dual-engine + arrow). Own engine is
+> the runtime; `@floating-ui` is out of the library (devDep, for the demo + parity
+> oracle); the native CSS-anchor path + `avoidCollisions:'flip'` shipped. Nothing
+> below is a to-do.
 
 ## Why