feat: uuid ids everywhere, pickers for linked tickets, @pi/ui checkboxes

- Postgres: every table has a uuid `id` (gen_random_uuid()); the event
  store keeps its relay order in `seq`, and the lookup tables their
  uniqueness in constraints of their own.
- MongoDB: `_id` is Mongo's ObjectId; `id` is the domain id (the same
  uuid as the aggregate's stream in Postgres), unique, and every query
  goes by it. Production starts from empty databases.
- Web: linking tickets and hanging one from a parent are picked from a
  searchable select (links across projects, parents within the project)
  instead of typing a key; every checkbox is @pi/ui's pi-checkbox.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

libs/api/shared/infrastructure/src/lib/event-store/entities/event.entity.ts

@@ -2,6 +2,7 @@ import {
   Column,
   CreateDateColumn,
   Entity,
+  Generated,
   Index,
   PrimaryGeneratedColumn,
   Unique,
@@ -13,12 +14,21 @@ import {
  */
 @Entity('events')
 @Unique('uq_events_stream_position', ['streamId', 'position'])
-@Index('idx_events_unpublished', ['id'], { where: '"published_at" IS NULL' })
+@Index('idx_events_unpublished', ['seq'], { where: '"published_at" IS NULL' })
 export class EventEntity {
-  /** Global order of the store, used to relay events in sequence. */
-  @PrimaryGeneratedColumn('increment', { type: 'bigint' })
+  /** The event's own id. */
+  @PrimaryGeneratedColumn('uuid')
   id!: string;
 
+  /**
+   * Global order of the store, used to relay events in sequence. A uuid has
+   * no reliable order, so it is kept apart.
+   */
+  @Index('uq_events_seq', { unique: true })
+  @Column({ type: 'bigint' })
+  @Generated('increment')
+  seq!: string;
+
   @Column({ name: 'stream_id', length: 64 })
   streamId!: string;
 

libs/api/shared/infrastructure/src/lib/event-store/event-store.relay.ts

@@ -73,7 +73,7 @@ export class EventStoreRelay
         .getRepository(EventEntity)
         .createQueryBuilder('e')
         .where('e.published_at IS NULL')
-        .orderBy('e.id', 'ASC')
+        .orderBy('e.seq', 'ASC')
         .limit(BATCH_SIZE)
         .setLock('pessimistic_write')
         .setOnLocked('skip_locked')