feat(launcher): add sync command to merge stats and history between machines over SSH

subminer sync <host> exchanges VACUUM INTO snapshots over ssh/scp and each
side merges the other's data as an insert-only union keyed on session UUIDs,
video keys, series title keys, and word/kanji identity. Lifetime totals and
daily/monthly rollups are applied incrementally so pre-retention history
survives, remote-only historical rollups are copied, and re-syncing is
idempotent. sync --snapshot/--merge expose the underlying steps for manual
transfers; a pid-file/mpv-socket guard refuses to run while SubMiner may be
writing the database and schema-version mismatches abort the merge.

launcher/config/cli-parser-builder.ts

@@ -38,6 +38,14 @@ export interface CliInvocations {
   statsCleanupVocab: boolean;
   statsCleanupLifetime: boolean;
   statsLogLevel: string | null;
+  syncTriggered: boolean;
+  syncHost: string | null;
+  syncSnapshotPath: string | null;
+  syncMergePath: string | null;
+  syncRemoteCmd: string | null;
+  syncDbPath: string | null;
+  syncForce: boolean;
+  syncLogLevel: string | null;
   doctorTriggered: boolean;
   doctorLogLevel: string | null;
   doctorRefreshKnownWords: boolean;
@@ -98,6 +106,7 @@ function getTopLevelCommand(argv: string[]): { name: string; index: number } | n
     'dictionary',
     'dict',
     'stats',
+    'sync',
     'texthooker',
     'app',
     'bin',
@@ -160,6 +169,14 @@ export function parseCliPrograms(
   let statsCleanupVocab = false;
   let statsCleanupLifetime = false;
   let statsLogLevel: string | null = null;
+  let syncTriggered = false;
+  let syncHost: string | null = null;
+  let syncSnapshotPath: string | null = null;
+  let syncMergePath: string | null = null;
+  let syncRemoteCmd: string | null = null;
+  let syncDbPath: string | null = null;
+  let syncForce = false;
+  let syncLogLevel: string | null = null;
   let doctorLogLevel: string | null = null;
   let doctorRefreshKnownWords = false;
   let logsTriggered = false;
@@ -289,6 +306,36 @@ export function parseCliPrograms(
       statsLogLevel = typeof options.logLevel === 'string' ? options.logLevel : null;
     });
 
+  commandProgram
+    .command('sync')
+    .description('Sync stats and watch history with another machine over SSH')
+    .argument('[host]', 'SSH destination (user@host or an ssh config alias)')
+    .option('--snapshot <file>', 'Write a consistent snapshot of the local stats database')
+    .option('--merge <file>', 'Merge a snapshot database file into the local stats database')
+    .option('--db <file>', 'Override the local stats database path')
+    .option('--remote-cmd <cmd>', 'subminer command to run on the remote host')
+    .option('-f, --force', 'Skip the running-app safety check')
+    .option('--log-level <level>', 'Log level')
+    .action((host: string | undefined, options: Record<string, unknown>) => {
+      const snapshot = typeof options.snapshot === 'string' ? options.snapshot.trim() : '';
+      const merge = typeof options.merge === 'string' ? options.merge.trim() : '';
+      const modes = [Boolean(host), Boolean(snapshot), Boolean(merge)].filter(Boolean).length;
+      if (modes === 0) {
+        throw new Error('Sync requires a host, --snapshot <file>, or --merge <file>.');
+      }
+      if (modes > 1) {
+        throw new Error('Sync host, --snapshot, and --merge cannot be combined.');
+      }
+      syncTriggered = true;
+      syncHost = host?.trim() || null;
+      syncSnapshotPath = snapshot || null;
+      syncMergePath = merge || null;
+      syncRemoteCmd = typeof options.remoteCmd === 'string' ? options.remoteCmd.trim() || null : null;
+      syncDbPath = typeof options.db === 'string' ? options.db.trim() || null : null;
+      syncForce = options.force === true;
+      syncLogLevel = typeof options.logLevel === 'string' ? options.logLevel : null;
+    });
+
   commandProgram
     .command('doctor')
     .description('Run dependency and environment checks')
@@ -400,6 +447,14 @@ export function parseCliPrograms(
       statsCleanupVocab,
       statsCleanupLifetime,
       statsLogLevel,
+      syncTriggered,
+      syncHost,
+      syncSnapshotPath,
+      syncMergePath,
+      syncRemoteCmd,
+      syncDbPath,
+      syncForce,
+      syncLogLevel,
       doctorTriggered,
       doctorLogLevel,
       doctorRefreshKnownWords,