pivot_layouts.source_name had a FK to sources(name) preventing stack names
from being used as layout keys. Dropped the FK so any view name works.
- database/migrate_pivot_layouts_drop_fk.sql: drop the FK constraint
- api/routes/stacks.js: add GET/POST/DELETE /:name/layouts routes
- ui/src/api.js: add getStackPivotLayouts / saveStackPivotLayout / deleteStackPivotLayout
- ui/src/pages/Pivot.jsx: use DB for stack layouts instead of localStorage;
collapse source/stack branches into saveLayout/deleteLayout helpers
- CLAUDE.md: document pivot layout persistence pattern
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
