Stop snapshotting the page; own the wheel gesture; one-row phone nav

Selection markers, tab panels, brand changes and theme changes no longer use
a view transition. The page snapshot could not blur what sits behind frosted
glass, so every frosted surface went clear for the length of the change.
nv.transition now measures the marker before and after, and animates the
marker itself (FLIP); arriving content animates on its own; colours fade on
their own surfaces. Verified in Firefox: no view transition is ever started.

Time picker: wheels take every pointer type (mouse, pen, touch) with
touch-action: none, so a phone, a browser's phone mode and a desktop behave
alike. The rubber-band is capped at about 40% of a row (a whole row made the
neighbour look selected). Each wheel has its own frame slot, so one wheel can
no longer swallow another's last scroll event. Switching 24H / AM / PM
happens when the wheel settles, and the hours animate into the new layout.

Carousel arrows are frosted glass, as anything floating over content should be.
At phone width the top bar keeps to one row and its link list scrolls.

GUIDELINES.md records the new cross-engine rules.

check.py, build.py and build.py --check pass.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

REFERENCE.md

@@ -488,7 +488,7 @@ everything still renders — state changes simply arrive instead of travelling.
 
 | Function | Signature | Does |
 | --- | --- | --- |
-| `nv.transition` | `(update, { direction, kind, scope }) => Promise` | Runs `update` inside a view transition so the change can be followed. `direction` is `"forward"`/`"backward"`; `kind: "theme"` slows the cross-fade; `scope` is the selection group (or list of groups) whose marker should travel — pass the group whose `aria-current`/`aria-selected` the update moves. Without `scope` nothing is lifted and the change cross-fades in place. Falls back to running `update` directly under reduced motion or without API support. |
+| `nv.transition` | `(update, { direction, kind, scope, content }) => Promise` | Runs `update` so the change can be followed, **without snapshotting the page**: a snapshot flattens frosted glass for its duration. `scope` is the selection group (or list of groups) whose marker should travel — the marker is measured before and after `update` and animated between the two boxes. `content` is an element (or list) that arrives from the side `direction` (`"forward"`/`"backward"`) names, or rises into place. `kind: "theme"` and reduced motion run `update` directly: surfaces transition their own colours. |
 | `nv.setTheme` | `("light" \| "dark" \| "system") => Promise` | Cross-fades the whole surface into the new appearance and fires `nv:theme` on `<html>`. |
 | `nv.syncThemeControls` | `(theme) => void` | Sets `aria-pressed` on every `[data-nv-theme]`. |
 | `nv.openDialog` | `(dialog \| id, trigger?) => dialog` | `showModal()`, plus a transform origin so the dialog expands out of its trigger. |
@@ -498,7 +498,7 @@ everything still renders — state changes simply arrive instead of travelling.
 | `nv.initTimePicker` | `(el) => void` | Builds and drives one `[data-nv-timepicker]`. |
 | `nv.initListbox` | `(list) => void` | Wires one `.nv-menu--listbox` (needs an `id` and a trigger with that `popovertarget`). |
 | `nv.initScroller` | `(frame) => void` | Wires one scroller's controls. |
-| `nv.liftLabels` | `(scope) => Element[]` | Names the navigation items in `scope` so a travelling marker passes behind them, and returns them. `nv.transition` does this for its `scope` and removes the names afterwards. |
+| `nv.liftLabels` | `(scope) => Element[]` | Names the navigation items in `scope`. Only for code that starts its own view transition; `nv.transition` no longer needs it. |
 | `nv.wire` | `(scope = document) => void` | Applies all of the below, and starts watching `.nv-reveal` / `.nv-reveal-group`. Runs once on load; call again after injecting markup. |
 | `nv.prefersReducedMotion` | `() => boolean` | |
 
@@ -530,20 +530,16 @@ everything still renders — state changes simply arrive instead of travelling.
 | `data-nv-tristate` | `input[type=checkbox]` | Click cycles unchecked → checked → partial. `="partial"` starts partial. Exposes `data-nv-state` (`off`/`on`/`partial`). |
 | `data-nv-scroller` | `.nv-scroller-frame` | Wires its `[data-nv-scroll="prev"\|"next"]` controls. |
 | `data-scrolled` | `.nv-nav` | Set by the application on scroll; gives the bar its shadow. |
-| `data-nv-direction` | `<html>` | Set during a transition by `nv.transition`. |
-| `data-nv-transition` | `<html>` | `"theme"` during an appearance change. |
+| `data-nv-direction` | `<html>` | Set during a view transition that application code starts itself. |
+| `data-nv-transition` | `<html>` | `"theme"` during a view transition the application starts for an appearance change. |
 | `data-nv-reveal` | revealed element | `pending` while waiting to scroll into view, `shown` while arriving; removed once it has. Set by `niveus.js`. |
-| `data-nv-travelling` | selection group | Set by `nv.transition` on each `scope` for the length of the change; names its marker. |
+| `data-nv-travelling` | selection group | Names the marker for a view transition the application starts itself. |
 
 ---
 
 ## Rules that bite
 
-1. **`view-transition-name` must be unique per document.** A duplicate makes
-   the browser skip the transition entirely. Markers are only named while their
-   group is in `scope`, so this only bites when one transition moves two groups
-   at once: give each its own `--nv-selection-name`. `.nv-nav-tabs` defaults
-   to `nv-tabs-selection` and everything else to `nv-selection`.
+1. **Do not start your own view transition around a page that has glass.** The snapshot cannot blur what sits behind frosted surfaces, so they go clear for its duration. Use `nv.transition`, which never snapshots the page. (If you must, `view-transition-name` has to be unique per document, or the browser skips the transition; give each selection group its own `--nv-selection-name`.)
 2. **A menu and its trigger must name the same anchor** through `--nv-anchor`,
    and the value must be unique per pair.
 3. **Hide inactive `.nv-tab-panel`s with `hidden`.** `nv.selectTab` relies