Add paging feature design spec

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

docs/superpowers/specs/2026-03-22-paging-design.md

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+# Paging Feature Design
+
+## Overview
+
+Introduce offset-based pagination to the admin post list and the generated static site (both post listings and category listings).
+
+## Data Layer
+
+### New `sites` column
+
+Add `posts_per_page INTEGER NOT NULL DEFAULT 10` to the `sites` table. This setting controls the number of posts per page on the **generated static site only**.
+
+### New SQL queries
+
+- `CountPostsOfSite(siteID, showDeleted)` — returns total post count for the site
+- `CountPostsOfCategory(categoryID)` — returns total published post count for a category
+
+### Model changes
+
+**`models.Site`** — add field:
+```go
+PostsPerPage int
+```
+
+**New shared type** (`models/paging.go`):
+```go
+type PageInfo struct {
+    CurrentPage  int
+    TotalPages   int
+    PostsPerPage int
+}
+```
+
+Existing `db.PagingParams` and queries (`SelectPostsOfSite`, `SelectPostsOfCategory`) already support `LIMIT/OFFSET` and remain unchanged.
+
+## Admin Section
+
+### Post list pagination
+
+- **Page size: hardcoded at 25** (not tied to the `PostsPerPage` site setting)
+- Handler (`handlers/posts.go` `Index()`) reads a `page` query parameter (default 1)
+- Computes offset as `(page - 1) * 25`
+- Fetches total post count via new `CountPosts()` service method to build `PageInfo`
+- Passes `PageInfo` to template
+
+### Service changes
+
+- `ListPosts()` accepts paging params from the handler instead of hardcoding them
+- New `CountPosts()` method that calls the count query
+
+### Template (`views/posts/index.html`)
+
+- Full numbered pagination with Previous/Next below the post list: `< 1 2 3 ... 10 >`
+- Preserves existing query params (e.g. `?filter=deleted`) when paginating
+- Both regular post list and trash view are paginated
+
+### Site settings form
+
+- Add "Posts per page" number input to `views/sitesettings/general.html`
+- Add `PostsPerPage` field to `UpdateSiteSettingsParams`
+- Server-side validation: minimum 1, maximum 100
+
+## Generated Static Site
+
+### URL structure
+
+Post listing pages:
+- `/posts/` — page 1
+- `/posts/page/2/` — page 2
+- `/posts/page/N/` — page N
+
+Category listing pages:
+- `/categories/<slug>/` — page 1
+- `/categories/<slug>/page/2/` — page 2
+- `/categories/<slug>/page/N/` — page N
+
+### Site root
+
+`/` (site root) shows the same content as `/posts/` (page 1 of all posts).
+
+### Builder changes (`providers/sitebuilder/builder.go`)
+
+- Instead of rendering one `posts_list.html` with all posts, generate multiple page files
+- Uses `site.PostsPerPage` from the site setting to determine page size
+- Same pattern for category pages
+
+### Publisher changes (`services/publisher/iter.go`)
+
+- Existing iterator fetches posts in batches of 50 internally — this stays as-is
+- The builder chunks posts into pages of `PostsPerPage` size and renders each page as a separate HTML file
+
+### Template (`layouts/simplecss/templates/posts_list.html`)
+
+- Receives `PageInfo` plus the posts for that page
+- Renders **Previous / Next** links only (no numbered pagination)
+- Previous link hidden on page 1; Next link hidden on last page
+
+## Approach
+
+Offset-based pagination using the existing `db.PagingParams` infrastructure. Page number maps to offset: `offset = (page - 1) * postsPerPage`.