fix: avoid history reclamation during structure-only upgrades

Ordinary database schema upgrades previously ran VACUUM on free pages and
showed misleading history-cleanup progress. Separate structure upgrades from
required legacy conversions, retaining reclamation intent only for retries
within the same startup. Preserve released data without new schema versions
or persistent migration markers; Agent and normal writes remain unchanged.

Add real SQLite and Worker regressions, bilingual operation-specific startup
copy, and migration documentation. Synchronize native Electron drag input
with actual resize state without weakening layout assertions.

Validation: 47 focused migration tests passed; typecheck, lint and diff checks
passed. Final full suite: 5137 passed, 74 skipped, 2 unrelated Electron failures.
Both failing Electron tests passed an isolated rerun; full CI remains unverified.

Release note: 修复普通数据库结构升级再次整理历史和回收空间的问题；仅在需要转换旧数据时执行相关处理，启动页准确显示当前升级操作。

src/shared/assistant-storage-contracts.ts

@@ -1,7 +1,7 @@
 import { z } from 'zod'
 
 export const assistantStorageProgressSchema = z.object({
-  stage: z.enum(['scanning', 'converting', 'compacting', 'complete', 'failed']),
+  stage: z.enum(['upgrading', 'scanning', 'converting', 'compacting', 'complete', 'failed']),
   processed: z.number().int().nonnegative(),
   total: z.number().int().nonnegative(),
   bytesBefore: z.number().nonnegative(),