- Add /api/template route group: GET, PUT /, POST/PUT/DELETE items, PUT items/reorder
- Add POST /api/budgets/generate before /{id} routes to avoid chi treating 'generate' as an id param
- /items/reorder registered before /items/{itemId} for correct static-before-param routing
- Create 002_templates.sql: item_tier enum, ALTER budget_items, templates and template_items tables with CHECK constraint
- Add ItemTier type with fixed/variable/one_off constants to models.go
- Add ItemTier field to BudgetItem struct
- Add Template, TemplateItem, TemplateDetail structs