Add article publish date to list and reader views

Extract publication dates from HTML meta tags when saving articles
and display them prominently in the article list and reader header.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/lib/db/schema.ts

@@ -42,6 +42,7 @@ export const articles = sqliteTable("articles", {
   updatedAt: integer("updated_at", { mode: "timestamp" }).$defaultFn(() => new Date()),
   readAt: integer("read_at", { mode: "timestamp" }),
   finishedAt: integer("finished_at", { mode: "timestamp" }), // When reading was completed
+  publishedAt: integer("published_at", { mode: "timestamp" }), // Original article publish date
 });
 
 // Highlights and notes