fix: the header carries what it promised, and nothing it does not

The registry's item described pickers the breadcrumb no longer has: nine fields — the
editability flags, the change callbacks, the navigation hook — that nothing read, while
the flow editor passed eight of them and quietly lost its inline rename. The type now
says what the bar does: a path, and either a summary or the page's own control for one.
The flow editor renames through that control, as the detail page already did.

`barPlacement` went the same way: no page registered 'inline', so the layout's guard
never fired.

The sessions page registered an inset of 0 whenever its preview pane never mounted —
the "no session selected" and opted-out arms — and 0 reads as "a page owns the right
edge", floating the band over the page's first line. It registers an inset only once
the pane has a width.

The band's sidebar handle docks through `setDetached` like the card's own toggle, so
docking still suppresses the rail's entry animation and closes the card; a summary
without its breadcrumb no longer leads with a stray separator in an embed; a page's
hint sits with its name whichever way the page named itself; and `Menu.closeInstantly`
and `EditorHeader`'s `inline`/`hideSummary` go, their callers having been replaced.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

frontend/src/lib/components/apps/editor/InWorkspaceAppViewer.svelte

@@ -156,10 +156,7 @@
 {#if canWriteApp && !hideEditBtn}
 	<!-- The page header carries it, with the app's name: a floating button over the app's own
 	     canvas lands on whatever the app draws there. -->
-	<PageHeaderContent
-		item={{ kind: 'app', path, raw_app: true, summaryEditable: false, pathEditable: false }}
-		actions={editAction}
-	/>
+	<PageHeaderContent item={{ kind: 'app', path }} actions={editAction} />
 {/if}
 
 {#snippet editAction()}