feat(lotw): full/incremental sync modes with live progress and time estimate

Two explicit sync buttons in the LoTW dialog:
- Full sync: qso_qslsince=2000-01-01, fresh report replaces all stored data.
- Incremental merge: since=last successful sync date, merged into the stored
  set (grids union, QSOs deduped by call + time). First sync / callsign change
  automatically falls back to full replace so no stale grids from another
  account linger.

Progress & estimates:
- Report body is now streamed; the header's <APP_LoTW_NUMREC> gives the real
  QSL count, total size is estimated as NUMREC * 720 B (measured), and the UI
  shows a determinate bar with 'N QSOs, ~X s remaining' once known.
- Pre-sync hint shows the measured rate (~8 s per 100 QSOs).
- readTimeout raised to 600 s (stall timeout, not a total cap — huge accounts
  legitimately take 30+ min at ARRL's ~10 KB/s stream rate); connectTimeout
  raised to 60 s (a busy server took 36.5 s to accept a connection).

Also: ISettingsRepo gains last-sync date/callsign bookkeeping, and the mutual
test fake implements the new members.

core/presentation/src/main/res/values-zh/strings.xml

@@ -165,6 +165,18 @@
     <string name="prefs_lotw_syncing">同步中…</string>
     <string name="prefs_lotw_configured">已从 LoTW 同步 — 共 %1$d 个网格</string>
     <string name="prefs_lotw_not_configured">未配置 — 直接登录 ARRL LoTW 拉取已确认 QSO 的网格，无需自建服务器</string>
+    <string name="lotw_sync_error_not_configured">LoTW 呼号/密码未配置</string>
+    <string name="lotw_sync_error_credentials">LoTW 同步失败——呼号或密码错误</string>
+    <string name="lotw_sync_error_rate_limited">LoTW 同步失败——服务器限流，请等几分钟后再试</string>
+    <string name="lotw_sync_error_timeout">LoTW 同步失败——连接超时，请更换网络重试</string>
+    <string name="lotw_sync_error_network">LoTW 同步失败——网络错误（%1$s）</string>
+    <string name="lotw_sync_full">全量同步</string>
+    <string name="lotw_sync_incremental">增量合并</string>
+    <string name="lotw_sync_rate_hint">下载速度约每 100 条 QSO 需 8 秒（另有 5–40 秒服务器生成时间）</string>
+    <string name="lotw_sync_progress_connecting">正在连接 LoTW 服务器…</string>
+    <string name="lotw_sync_progress_downloading">正在下载报告…</string>
+    <string name="lotw_sync_progress_count">本次同步 %1$d 条 QSO…</string>
+    <string name="lotw_sync_progress_qso">本次同步 %1$d 条 QSO，预计还需 %2$d 秒</string>
     <string name="prefs_locator_text">使用梅登黑德网格设置站点位置</string>
 
     <string name="prefs_data_title">卫星数据更新</string>

core/presentation/src/main/res/values/strings.xml

@@ -200,6 +200,18 @@
     <string name="prefs_lotw_syncing">Syncing…</string>
     <string name="prefs_lotw_configured">Synced from LoTW — %1$d grids total</string>
     <string name="prefs_lotw_not_configured">Not configured — pull confirmed grids directly from ARRL LoTW, no self-hosted server needed</string>
+    <string name="lotw_sync_error_not_configured">LoTW callsign/password not configured</string>
+    <string name="lotw_sync_error_credentials">LoTW sync failed — callsign or password incorrect</string>
+    <string name="lotw_sync_error_rate_limited">LoTW sync failed — rate limited by server, wait a few minutes and retry</string>
+    <string name="lotw_sync_error_timeout">LoTW sync failed — connection timed out, try another network</string>
+    <string name="lotw_sync_error_network">LoTW sync failed — network error (%1$s)</string>
+    <string name="lotw_sync_full">Full sync</string>
+    <string name="lotw_sync_incremental">Incremental merge</string>
+    <string name="lotw_sync_rate_hint">Download runs at ~8 s per 100 QSOs (plus 5–40 s server generation time)</string>
+    <string name="lotw_sync_progress_connecting">Connecting to LoTW…</string>
+    <string name="lotw_sync_progress_downloading">Downloading report…</string>
+    <string name="lotw_sync_progress_count">Syncing %1$d QSOs…</string>
+    <string name="lotw_sync_progress_qso">Syncing %1$d QSOs, ~%2$d s remaining</string>
     <string name="prefs_locator_text">Set station\'s position using locator</string>
 
     <string name="prefs_data_title">Satellite data</string>