[adithya-s-119]

Summary

Follow-up to #361. Two remaining SMB problems:

• Domain accounts could never authenticate. smb2 passes the account name and domain to NTLM separately, but Flick only has one username field and was sending DOMAIN\user (or user@domain) as the account with an empty domain. Those forms are now split into the pieces a Windows client sends. Plain local usernames are unchanged.
• An interrupted library walk discarded everything it had already listed. The Dart side collected entries while the Rust stream walked the share, then only imported them after the stream finished. A Wi-Fi drop or session expiry halfway through meant zero new rows on a first sync, even though most of the library had been listed.

Behavior now

• On a complete walk: import, purge stale rows, stamp lastSyncedAt (unchanged).
• On an interrupted walk: import the entries already collected, skip the purge and lastSyncedAt stamp (unseen files are not stale), log an allowlisted result=partial record, and still surface the scan failure so the user can retry and complete it.
• DOMAIN\user, user@domain, plain user, guest, and malformed separator input are covered by Rust unit tests.

Related issue

Refs #291.

Testing

• flutter analyze --no-fatal-infos: no errors or warnings (same 28 pre-existing infos as main).
• flutter test test/services/smb_service_parse_test.dart test/services/smb_service_download_test.dart test/services/network_cache_service_test.dart test/services/remote_metadata_backfill_test.dart: 38 passed.
• Rust SMB module in an isolated crate against smb2 0.27.2: 8 passed, including the new account-format tests. Full cargo test is blocked on this Windows host by the existing soundtouch-sys C++ build issue.
• Not hardware-tested: no Android device or SMB share available here.

Checklist

• flutter analyze passes
• flutter test passes (SMB/network suites pass; full Windows run has pre-existing failures)
• Rust changes: cargo test --manifest-path rust/Cargo.toml passes (SMB module tests pass in isolation; full run blocked by existing soundtouch build issue on this host)
• Built and ran the app if the change touches a playback path (not run; no device/share available)
• Generated code regenerated and committed if bridge/drift/freezed models changed (none required)
• CHANGELOG.md updated for user-facing changes
• No secrets, keys, tokens, or machine-local files committed
• One change per PR; no unrelated reformatting in the same diff
• Hardware tested if the Rust audio engine or USB/DAC output changed (SMB module only)

[ultraelectronica]

Reviewed and approved for versionF testing.

• Rust: split_account is unit-tested for plain, DOMAIN\user, user@domain, and malformed inputs; all 8 SMB tests and the full 369-test host suite pass.
• Dart: partial walks import collected entries before rethrowing, and skip purge/lastSyncedAt so unseen files are not treated as stale. Targeted SMB/cache/backfill suites pass (38 tests).
• CI: all checks green (4 Android Rust targets, host Rust tests, Flutter analyze + test).
• Local full Flutter run: 1222 passed; only webdav_sync_integration_test.dart failed to load due to a pre-existing local Isar Core version mismatch (required 3.3.2, found 3.4.1), unrelated to this PR.
• Hardware SMB validation (especially domain/UPN accounts) still pending; that is what versionF is for.