feat(ui): add maintenance page for task management

* Implement maintenance page with task and log display
* Add backfill and metadata retry functionality
* Integrate grid component for project display in thoughts page
* Update types for maintenance tasks and logs
* Enhance sidebar and shell for new maintenance navigation

migrations/_old/004_create_thought_links.sql

@@ -0,0 +1,10 @@
+create table if not exists thought_links (
+  from_id    bigint      not null references thoughts(id) on delete cascade,
+  to_id      bigint      not null references thoughts(id) on delete cascade,
+  relation   text        not null,
+  created_at timestamptz default now(),
+  primary key (from_id, to_id, relation)
+);
+
+create index if not exists thought_links_from_idx on thought_links (from_id);
+create index if not exists thought_links_to_idx on thought_links (to_id);