Add post tags, with a tag page and two side-column modules

Posts can now carry tags, set on the post form as a checklist of the
blog's existing tags plus a comma-separated box for new ones (no JS).
A tag is a name and a unique slug, so "Go" and "go" are one tag and
Greek tags get readable URLs; tags no post uses any more are deleted.

On the blog, tags appear under the post date and link to /tag/<slug>,
which lists the published posts from every page, paginated like a page.
Two new layout modules show them: a Tags list (with counts, by use) and
a Tag cloud (alphabetical, sized by use). Both are only fetched when a
visible module needs them.

The article loop and pager move to a shared postlist partial; while
there, the pager stops adding a trailing slash — /news/?p=2 was a 404
because a {page} wildcard never matches one.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Sd8UPWrvyYCLj97JexNw3A

1 files changed, 15 insertions, 4 deletions

diff --git a/internal/store/posts.go b/internal/store/posts.go
index 569640b..706d132 100644
--- a/internal/store/posts.go
+++ b/internal/store/posts.go
@@ -18,16 +18,25 @@ type Post struct {
 	// joined
 	PageSlug  string
 	PageTitle string
+	Tags      []Tag // by name; IDs are not loaded
 }
 
-const postCols = `p.id, p.page_id, p.slug, p.title, p.body_md, p.body_html, p.published, p.created_at, p.updated_at, g.slug, g.title`
+// The tags come along as two parallel arrays (names and slugs, both by name)
+// so every post query stays a single round trip; the alias p is the posts row.
+const postCols = `p.id, p.page_id, p.slug, p.title, p.body_md, p.body_html, p.published, p.created_at, p.updated_at, g.slug, g.title,
+	coalesce((SELECT array_agg(t.name ORDER BY t.name) FROM post_tags pt JOIN tags t ON t.id=pt.tag_id WHERE pt.post_id=p.id), '{}'),
+	coalesce((SELECT array_agg(t.slug ORDER BY t.name) FROM post_tags pt JOIN tags t ON t.id=pt.tag_id WHERE pt.post_id=p.id), '{}')`
 
 func scanPost(row interface{ Scan(...any) error }) (*Post, error) {
 	var p Post
-	err := row.Scan(&p.ID, &p.PageID, &p.Slug, &p.Title, &p.BodyMD, &p.BodyHTML, &p.Published, &p.CreatedAt, &p.UpdatedAt, &p.PageSlug, &p.PageTitle)
+	var names, slugs []string
+	err := row.Scan(&p.ID, &p.PageID, &p.Slug, &p.Title, &p.BodyMD, &p.BodyHTML, &p.Published, &p.CreatedAt, &p.UpdatedAt, &p.PageSlug, &p.PageTitle, &names, &slugs)
 	if err != nil {
 		return nil, wrap(err)
 	}
+	for i := range names {
+		p.Tags = append(p.Tags, Tag{Name: names[i], Slug: slugs[i]})
+	}
 	return &p, nil
 }
 
@@ -130,6 +139,8 @@ func (bs *BlogStore) UpdatePost(ctx context.Context, p *Post) error {
 }
 
 func (bs *BlogStore) DeletePost(ctx context.Context, id int64) error {
-	_, err := bs.db.Exec(ctx, `DELETE FROM posts WHERE id=$1`, id)
-	return err
+	if _, err := bs.db.Exec(ctx, `DELETE FROM posts WHERE id=$1`, id); err != nil {
+		return err
+	}
+	return deleteOrphanTags(ctx, bs.db)
 }