preview: full-screen modal replaces inline split + tags route reorg

The old SplitGrid + InlinePreview pane is replaced by a full-screen
PreviewModal mounted once at the layout root. Open via Space on the
focused tile or double-click; close on Esc (or X / Space again).
Inside, PreviewPane renders the focused photo, RightSidebar carries
the metadata, BulkActionBar reuses the existing per-photo actions,
and PreviewCarousel windows ±50 thumbs around the focused index.

Selection contract matches the grid: plain click reduces, shift
extends the range, ⌘/Ctrl toggles, plain arrow drops the multi-
selection, shift-arrow extends. New clearBulkToFirst() helper makes
Esc / Clear collapse a bulk back to single-focus on its first member
before the next press fully dismisses (modal closes, grid clears
focus).

Tags route reorganised into /tags/[category]/[[value]] with its own
+layout and TagsBrowserSidebar; the old monolithic /tags/+page is
trimmed to a legacy redirect.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/src/lib/actions/gridKeyNav.ts

@@ -13,6 +13,7 @@ import {
 import { queryClient } from '$lib/queryClient';
 import { filters } from '$lib/stores/filters.svelte';
 import {
+	clearBulkToFirst,
 	clearSelection,
 	focusAfter,
 	indexOf,
@@ -23,7 +24,7 @@ import {
 	toggle
 } from '$lib/stores/selection.svelte';
 import { popAndRun, push as pushUndo } from '$lib/stores/undo.svelte';
-import { toggleLeftSidebar, toggleRightSidebar } from '$lib/stores/view.svelte';
+import { openPreview, toggleLeftSidebar, toggleRightSidebar, view } from '$lib/stores/view.svelte';
 import type { PpPhoto } from '$lib/types/photoprism';
 
 /**
@@ -381,6 +382,24 @@ export function gridKeyNav(node: HTMLElement, params: GridKeyNavParams = {}) {
 		const tag = (e.target as HTMLElement | null)?.tagName?.toLowerCase();
 		if (tag === 'input' || tag === 'textarea' || tag === 'select') return;
 
+		// Modal owns arrow / Escape / Space while it's open — it handles
+		// its own linear nav, close-on-Esc, and close-on-Space. Action
+		// keys (X/S/U/A/Z) still pass through because they target the
+		// shared selection store and work the same in either context.
+		if (view.previewOpen) {
+			if (
+				e.key === 'ArrowLeft' ||
+				e.key === 'ArrowRight' ||
+				e.key === 'ArrowUp' ||
+				e.key === 'ArrowDown' ||
+				e.key === 'Escape' ||
+				e.key === ' ' ||
+				e.code === 'Space'
+			) {
+				return;
+			}
+		}
+
 		// S+digit chord. A digit 1–9 within the chord window consumes the key
 		// and fires add-to-heap-N. Any other key cancels the chord without
 		// firing the default active-heap action — the user switched intent —
@@ -398,6 +417,18 @@ export function gridKeyNav(node: HTMLElement, params: GridKeyNavParams = {}) {
 		const meta = e.metaKey || e.ctrlKey;
 		const shift = e.shiftKey;
 
+		// Space on a focused tile opens the full-screen preview modal.
+		// Matches the dblclick gesture so the user has both keyboard and
+		// mouse paths to the same surface. `e.code === 'Space'` covers
+		// layouts where `e.key` is the dead-key combining mark.
+		if ((e.key === ' ' || e.code === 'Space') && !meta && !shift) {
+			if (selection.focused) {
+				e.preventDefault();
+				openPreview();
+				return;
+			}
+		}
+
 		// ── Grid nav keys ────────────────────────────────────────────────────
 		switch (e.key) {
 			case 'ArrowLeft':
@@ -424,6 +455,11 @@ export function gridKeyNav(node: HTMLElement, params: GridKeyNavParams = {}) {
 				}
 				return;
 			case 'Escape':
+				// First Esc collapses a multi-selection back to single-focus
+				// on its first member — the user's "starting photo" stays
+				// visible instead of vanishing. Only when there's no bulk
+				// does Esc fully dismiss focus.
+				if (clearBulkToFirst()) return;
 				clearSelection();
 				setFocused(null);
 				return;