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/research.md

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+# Research: Library Pagination UI
+
+## Decision: Angular Router query params for URL state
+
+**Decision**: Use `this.router.navigate([], { queryParams: { page: n }, queryParamsHandling: 'merge' })` for page navigation and `snapshot.queryParamMap.get('page')` on init.
+
+**Rationale**: The library component already uses Angular Router for `?tags=` query params (added in feature 007). Extending the same pattern to `?page=` is the natural fit and keeps a single source of truth in the URL. The `queryParamsHandling: 'merge'` flag ensures that navigating to a new page does not erase the active `?tags=` filter, and vice versa.
+
+**Alternatives considered**:
+- Component-local state only (no URL): rejected — FR-008 requires bookmarkable URLs
+- `queryParamsHandling: ''` (replace): rejected — would erase `?tags=` param when changing pages
+
+---
+
+## Decision: Replace `loadMore()` with `goToPage(page: number)`
+
+**Decision**: Remove `loadMore()`, `hasMore`, and the append pattern. Replace with `goToPage(n)` that sets `this.images = []` and loads from `offset = (page - 1) * limit`.
+
+**Rationale**: The spec requires discrete pages (FR-001, FR-006). Keeping `loadMore()` alongside pagination would create conflicting UX. Clean removal is simpler and avoids two code paths.
+
+**Alternatives considered**:
+- Keep `loadMore()` as a fallback: rejected — two navigation patterns in one view is confusing
+
+---
+
+## Decision: No new dependencies
+
+**Decision**: Implement using existing Angular Router, HttpClient, and CDR. No pagination library imported.
+
+**Rationale**: The pagination logic is trivial (previous/next buttons, a counter, clamped page index). Pulling in a library for two buttons and a text label adds bundle weight and a dependency for no meaningful gain.
+
+**Alternatives considered**:
+- `ngx-pagination`: rejected — overkill for two-button prev/next pattern