Feat: Replace Load More with Previous/Next pagination in library

Page size changes from 50 to 24. Library now shows discrete page navigation
with a "Page N of M" indicator, total image count, and URL state (?page=N)
so pages are bookmarkable and the browser Back button works. Tag filter
resets to page 1. Out-of-range page params are clamped silently.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

specs/015-library-pagination/contracts/pagination-query.md

@@ -0,0 +1,52 @@
+# Contract: Image List Pagination Query
+
+No new API endpoints are introduced. This document records the existing API contract the UI relies on for pagination.
+
+## Endpoint
+
+```
+GET /api/v1/images?limit={limit}&offset={offset}&tags={tags}
+```
+
+## Parameters
+
+| Parameter | Type    | Required | Description                                      |
+|-----------|---------|----------|--------------------------------------------------|
+| `limit`   | integer | No       | Images per page. UI sends `24`. Max is 100.      |
+| `offset`  | integer | No       | Number of images to skip. UI computes `(page-1) * 24`. |
+| `tags`    | string  | No       | Comma-separated tag names for AND-filter.        |
+
+## Response
+
+```json
+{
+  "items": [ /* ImageRecord[] */ ],
+  "total": 143,
+  "limit": 24,
+  "offset": 48
+}
+```
+
+| Field    | Type    | Description                                      |
+|----------|---------|--------------------------------------------------|
+| `total`  | integer | Total images matching the filter (all pages).    |
+| `limit`  | integer | Page size echoed back.                           |
+| `offset` | integer | Offset echoed back.                              |
+| `items`  | array   | Images for this page only.                       |
+
+## UI-Computed Values
+
+```
+totalPages = Math.ceil(total / limit)       // e.g. ceil(143 / 24) = 6
+currentPage = offset / limit + 1            // e.g. 48 / 24 + 1 = 3
+offset = (page - 1) * limit                // e.g. (3 - 1) * 24 = 48
+```
+
+## URL State
+
+| Query Param | Source              | Example          |
+|-------------|---------------------|------------------|
+| `page`      | current page number | `?page=3`        |
+| `tags`      | active tag filters  | `?tags=cat,funny` |
+
+Both params coexist: `/?page=3&tags=cat,funny`