Closes#43
Persist kagane cover bytes in a dedicated Postgres covers table keyed by image ID. The web handler reads storage before the browser, writes validated fetches through, and no longer keeps an in-process cover cache. Added migration, store persistence tests including reopen, handler coverage for stored/miss/rejected paths, and corrected repository guidance.
Verification:
- go test ./...
- CGO_ENABLED=0 go build ./...
Reviewed-on: #49
Co-authored-by: Sulthan Zaki <sultankiki05@gmail.com>
Co-committed-by: Sulthan Zaki <sultankiki05@gmail.com>
