feat(saas): industry agent template assignment system

Phase 1-8 of industry-agent-delivery plan:

- DB migration: accounts.assigned_template_id (ON DELETE SET NULL)
- SaaS API: 4 new endpoints (assign/get/unassign/create-agent)
- Service layer: assign_template_to_account, get_assigned_template, unassign_template, create_agent_from_template)
- Types: AssignTemplateRequest, AgentConfigFromTemplate (capabilities merged into tools)
- Frontend SaaS Client: assignTemplate, getAssignedTemplate, unassignTemplate, createAgentFromTemplate
- saasStore: assignedTemplate state + login auto-fetch + actions
- saas-relay-client: fix unused import and saasUrl reference error
- connectionStore: fix relayModel undefined error
- capabilities default to glm-4-flash

- Route registration: new template assignment routes

Cospec and handlers consolidated

Build: cargo check --workspace PASS, tsc --noEmit Pass

crates/zclaw-saas/migrations/20260403000001_accounts_template_assignment.sql

@@ -0,0 +1,9 @@
+-- Phase 1: accounts 表增加 assigned_template_id
+-- 用户选择行业模板后记录分配关系，用于跟踪和跳过 onboarding
+-- ON DELETE SET NULL: 模板被删除时不影响账户
+
+ALTER TABLE accounts ADD COLUMN assigned_template_id TEXT
+  REFERENCES agent_templates(id) ON DELETE SET NULL;
+
+COMMENT ON COLUMN accounts.assigned_template_id IS
+  '用户选择的行业模板 ID，用于跟踪模板分配状态';