feat: add paginated project discovery

hub/prisma/schema.prisma

@@ -46,6 +46,7 @@ model Organization {
   agentSkills                  OrganizationAgentSkill[]
   agentRoles                   OrganizationAgentRole[]
   auditEntries                 AuditEntry[]                    @relation("organizationAudit")
+  projectSearchDocuments      ProjectSearchDocument[]
 
   @@index([status])
 }
@@ -437,11 +438,17 @@ model ExternalPrincipalMembership {
 /// ADR-0021: transparent project explorer folder. Folders are org-scoped
 /// navigation/aggregation nodes, not permission resources; project grants stay
 /// attached to PROJECT resources.
+enum FolderKind {
+  REGULAR
+  SYSTEM_INBOX
+}
+
 model Folder {
   id             String    @id @default(cuid())
   organizationId String
   parentId       String?
   name           String
+  kind           FolderKind @default(REGULAR)
   sortKey        String    @default("")
   createdAt      DateTime  @default(now())
   updatedAt      DateTime  @updatedAt
@@ -460,6 +467,7 @@ model Project {
   id              String    @id @default(cuid())
   organizationId  String
   folderId        String?
+  code            String?
   name            String
   workspaceDir    String
   createdByUserId String?
@@ -477,12 +485,34 @@ model Project {
   roleTriggerGrants RoleTriggerGrant[]    @relation("projectRoleGrants")
   auditEntries      AuditEntry[]          @relation("projectAudit")
   fileChanges       AgentFileChange[]     @relation("projectFileChanges")
+  searchDocument    ProjectSearchDocument?
 
   @@index([organizationId, archivedAt])
   @@index([folderId, archivedAt])
   @@index([archivedAt])
 }
 
+/// Derived, rebuildable search projection for project discovery. PostgreSQL
+/// triggers keep it synchronized with Project and Folder mutations; Project
+/// remains the source of truth and authorization remains outside this table.
+model ProjectSearchDocument {
+  projectId             String   @id
+  organizationId        String
+  name                  String
+  code                  String?
+  normalizedCode        String
+  normalizedName        String
+  breadcrumb            String
+  normalizedBreadcrumb String
+  normalizedSearchText  String
+  updatedAt             DateTime @updatedAt
+
+  project      Project      @relation(fields: [projectId], references: [id], onDelete: Cascade)
+  organization Organization @relation(fields: [organizationId], references: [id], onDelete: Cascade)
+
+  @@index([organizationId])
+}
+
 /// ADR-0001 + ADR-0021: active bindings are one project ↔ one Feishu chat
 /// (1:1). Historical archived bindings are retained for audit; partial unique
 /// indexes in migrations enforce one active binding per project and per chat.