chore(deps): 升级 TanStack Start 至 1.167.48，移除 start-plugin-core patch

upstream 已修（PR #7249，1.169.4 拆分 vite/rsbuild subpath，
@rsbuild/core 列为 optional peer），patches/ 不再必要。

- @tanstack/react-start ^1.167.43 → ^1.167.48
- @tanstack/react-router ^1.168.23 → ^1.168.24
  (react-start@1.167.48 exact 依赖，避免 lockfile 双版本)
- 删除 patches/@tanstack%2Fstart-plugin-core@1.168.0.patch
- 删除 package.json patchedDependencies 块
- AGENTS.md 移除 patches/ layout 说明

验证：fix / typecheck / test / build / compile 均通过；
start-plugin-core@1.169.4 dist 不再静态 import rsbuild。

AGENTS.md

@@ -173,7 +173,6 @@ bin.ts                          # citty entry (root) — keep imports minimal (s
 compile.ts                      # `bun build --compile` driver; resolves --target; sets minify/bytecode/sourcemap
 embed-migrations.ts             # codegen: scans ./drizzle/meta/_journal.json → src/server/db/migrations.gen.ts
 drizzle/                        # SQL migrations (source of truth for `db:generate`; not shipped in binary)
-patches/                        # Bun `patchedDependencies` — patches `@tanstack/start-plugin-core` to drop the `@rsbuild/core` mis-import (see `package.json`)
 ```
 
 Nitro plugins are wired in `vite.config.ts` (`nitro({ plugins: [...] })`), not via a Nitro config file.