docs(snapshot): add V8 snapshot troubleshooting guide (#6010)

## Motivation

Building a V8 startup snapshot serializes the whole heap, so any
dependency that
opens a socket, starts a timer, or initializes a native binding at
module-evaluation time can make the blob fail to build — or build and
then crash
on restore. There was no guide for finding which module is responsible
or how to
fix it.

## What

New dedicated page `advanced/snapshot-troubleshooting.md` (EN + zh-CN):

- **The serializability rule** — what cannot survive the round-trip
(native
bindings / libuv handles / lazy web-global getters) and when a
dependency
  trips it.
- **Failure surfaces** — build-time vs restore-time, with the exact
error
  strings each emits (`killed by signal SIGSEGV`, `no blob was written`,
  `Check failed: current == end_slot_index`, `Aop Advice not found`,
  `Cannot find module`, …).
- **Find the offending module** — `NODE_DEBUG` namespaces, a clean
`NODE_OPTIONS`, `--dry-run`, `--skip-bundle` bisecting,
`--force-external`
  confirmation.
- **Fixes** — `--force-external`, `egg.snapshot.lazyModules`, the
snapshot
lifecycle hooks, deferring work out of module scope, avoiding the web
globals.
- **Failure modes in detail** (tegg `@Advice` filePath, the
lazy-external member
  proxy, runtime-asset `ENOENT`) and a configuration reference table.

Also documents the previously-undocumented `egg.snapshot.lazyModules`
config in
`advanced/snapshot.md`, cross-links the new page from it, and wires the
page into
the English and Chinese advanced sidebars.

Docs-only; no runtime code change. Builds on the snapshot feature
already on
`next` (#5998 / #5999 / #6001 / #6003).

## Test evidence

- `vitepress build site` passes clean — VitePress's dead-link/anchor
check is
green, so both new pages render and every cross-file and in-page anchor
resolves (the two detail headings use explicit ASCII `{#…}` ids because
the
  VitePress slugifier retains CJK + fullwidth `「」`).
- Every technical claim was adversarially verified against the
`egg-bundler` / `egg-bin` / `egg-scripts` source — exact error strings,
flag
  names, debug namespaces, and the default lazy-module set.

🤖 Generated with [Claude Code](https://claude.com/claude-code)


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Documentation**
* Added a new Snapshot Troubleshooting guide in English and Chinese,
covering common build and restore failure symptoms, how to diagnose
them, and recommended fixes.
* Expanded the Snapshot guide with guidance on configuring additional
lazy-loaded modules, plus clearer troubleshooting links.
* Updated the sidebar navigation to include the new troubleshooting page
in both languages.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: killagu

site/.vitepress/config.mts

@@ -292,6 +292,7 @@ function sidebarAdvanced(): DefaultTheme.SidebarItem[] {
         { text: 'Plugin Development', link: 'plugin' },
         { text: 'Framework Development', link: 'framework' },
         { text: 'V8 Startup Snapshot', link: 'snapshot' },
+        { text: 'Snapshot Troubleshooting', link: 'snapshot-troubleshooting' },
       ],
     },
   ];
@@ -406,6 +407,7 @@ function sidebarAdvancedZhCN(): DefaultTheme.SidebarItem[] {
         { text: '升级你的生命周期事件函数', link: 'loader-update' },
         { text: '对象生命周期', link: 'lifecycle' },
         { text: 'V8 启动快照', link: 'snapshot' },
+        { text: '快照故障排查', link: 'snapshot-troubleshooting' },
       ],
     },
   ];