feat(documents): paginate search with a Pagination control

Frontend side of the /documents pagination work. The page.server.ts load
reads ?page= from the URL, forwards page+size=50 to the backend, and
exposes the new totalElements/pageNumber/pageSize/totalPages fields on
`data`. +page.svelte renders a <Pagination> component below the result
list; buildPageHref preserves every filter param and only updates page.
The existing triggerSearch debounce flow intentionally drops `page`
when any filter changes, so filter edits reset to page 0 automatically.

<Pagination> uses plain <a href> links (not goto) so SvelteKit's default
scroll restoration scrolls new pages to the top — the expected senior-UX
behaviour. Decorative chevrons wrapped in aria-hidden spans, 44px touch
targets, focus-visible ring, stacks vertically under 640px. The control
hides itself when totalPages ≤ 1.

Test coverage: 9 cases on Pagination (label, aria-current, prev/next
enable/disable, makeHref invocation, decorative chevron, touch target),
plus a filter-reset assertion on +page.svelte (page 5 → edit q →
goto URL must drop page=). Adds i18n keys in de/en/es. Manual edit to
api.ts pending a post-merge npm run generate:api against a rebuilt
dev backend. (#315)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/lib/generated/api.ts

@@ -1921,7 +1921,13 @@ export interface components {
         DocumentSearchResult: {
             items: components["schemas"]["DocumentSearchItem"][];
             /** Format: int64 */
-            total: number;
+            totalElements: number;
+            /** Format: int32 */
+            pageNumber: number;
+            /** Format: int32 */
+            pageSize: number;
+            /** Format: int32 */
+            totalPages: number;
         };
         MatchOffset: {
             /** Format: int32 */
@@ -4032,6 +4038,16 @@ export interface operations {
                 dir?: string;
                 /** @description Tag operator: AND (default) or OR */
                 tagOp?: string;
+                /**
+                 * @description Page number (0-indexed)
+                 * @default 0
+                 */
+                page?: number;
+                /**
+                 * @description Page size (max 100)
+                 * @default 50
+                 */
+                size?: number;
             };
             header?: never;
             path?: never;