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, 26 insertions, 0 deletions

diff --git a/internal/db/migrations/blog/00004_tags.sql b/internal/db/migrations/blog/00004_tags.sql
new file mode 100644
index 0000000..a2ac86a
--- /dev/null
+++ b/internal/db/migrations/blog/00004_tags.sql
@@ -0,0 +1,26 @@
+-- +goose Up
+-- Tags are shared by posts. The slug is both the URL (/tag/<slug>) and the
+-- dedupe key, so "Go" and "go" are one tag (the first spelling is kept).
+CREATE TABLE tags (
+    id    bigserial PRIMARY KEY,
+    name  text NOT NULL,
+    slug  text NOT NULL UNIQUE
+);
+CREATE TABLE post_tags (
+    post_id  bigint NOT NULL REFERENCES posts(id) ON DELETE CASCADE,
+    tag_id   bigint NOT NULL REFERENCES tags(id) ON DELETE CASCADE,
+    PRIMARY KEY (post_id, tag_id)
+);
+CREATE INDEX post_tags_tag ON post_tags (tag_id);
+
+-- Two more layout modules: the tag list and the tag cloud.
+ALTER TABLE modules DROP CONSTRAINT modules_kind_check;
+ALTER TABLE modules ADD CONSTRAINT modules_kind_check
+    CHECK (kind IN ('title', 'logo', 'menu', 'archive', 'recent', 'html', 'rss', 'text', 'sitemap', 'tags', 'tagcloud'));
+
+-- +goose Down
+DELETE FROM modules WHERE kind IN ('tags', 'tagcloud');
+ALTER TABLE modules DROP CONSTRAINT modules_kind_check;
+ALTER TABLE modules ADD CONSTRAINT modules_kind_check
+    CHECK (kind IN ('title', 'logo', 'menu', 'archive', 'recent', 'html', 'rss', 'text', 'sitemap'));
+DROP TABLE post_tags, tags;