Refactor: extract reusable inventory components

[GitAddRemote]

Summary

• Extract reusable inventory components: InventoryInlineRow, InventoryNewRow, and InventoryFiltersPanel for shared inline editing, new-row entry, and filter/view controls.
• Wire Inventory page to use the new components while preserving Editor Mode behaviors: focus transitions, org guardrail, retry/dirty states, and validation messaging.
• Keep inline actions/focus, new-row retry, and org blocking intact; clean up page-level code for reuse.

Testing

• pnpm --filter frontend lint
• pnpm --filter frontend build
• pnpm --filter frontend test -- --runTestsByPath frontend/src/pages/Inventory.editor-mode.test.tsx