Move chunk search from DocumentsPage into a new Search bounded context
(features/search/) with its own store, API layer, page and route.
Clean search state out of the ingestion module.
Closes#159
Replace hardcoded 5 MB upload limit with a configurable setting.
Backend exposes the value via /api/health, frontend reads it
dynamically for validation and UI messages.
Closes#48
Replace generic orange "D" placeholders with the duck mascot logo
in all branding touchpoints: navbar header, home page hero, studio
import view, and browser favicon.
Introduce a feature-flags module in the frontend that detects
the backend conversion engine via /health and exposes typed
feature flags. Chunking is enabled only in local engine mode.
