Convert Discover, Feed, MyShows, and Settings pages from bespoke 3-column
flexbox JSX to render entirely via the shared <YaziPaneRow> parent|current|
preview primitive. Each page now supplies parent/current/preview content
accessors plus labels; the pane row handles layout, borders, focus styling,
and the muted placeholder for the blank parent slot at depth 0.
Replace Solid's children() helper in YaziPaneRow with a local normalizeContent
that hands the raw accessor to a reactive
expression. children() flattens to a stable resolved-nodes array and does not
re-resolve on truthy<->truthy root swaps (e.g. depth switching a pane's root
between a list fragment and an editor), which would freeze the previous
subtree. The insert effect from the reactive expression disposes and
remounts on element-identity change instead.
Add tests/yazi-pages-depth.test.ts covering the nav-store depth-stack
contract the pages depend on (push/pop stack growth, parent-slot data model
across root→child→grandchild→pop transitions).
