fix(sandbox): address PR #250 review — SSRF guard, eviction safety, cleanup (#243)

Security:
- stash_page: reject path-traversal / percent-encoded srcs before the authed
  loopback fetch (resolveInternalFilePath), closing an SSRF/exfiltration hole
  where a crafted node.attrs.src could read an arbitrary internal GET endpoint
  into the anonymous sandbox.

Stability:
- stash_page: revert + recount mirrors FIFO-evicted by a later put in the same
  stash (no dangling sandbox refs, honest images.mirrored/failed); free image
  blobs if the final document put throws.
- Reject/clamp non-positive SANDBOX_TTL_MS to the 1h default (warn once).
- Log mirror failures unconditionally (console.warn, no blob bodies).

Cleanup / architecture:
- Remove dead expiresAt from SandboxPutResult.
- Centralize the /api/sb route in SANDBOX_ROUTE_SEGMENT/SANDBOX_API_PATH and
  move URL composition into SandboxStore.putAndLink; drop the duplicated sink
  closures and the now-unused EnvironmentService injection from McpService and
  AiChatToolsService.
- Un-export isInternalFileUrl; document the process-local (instance-bound)
  sandbox limitation in the tool description and .env.example.

Docs/tests:
- README/README.ru: 38 -> 39 tools + stash_page entry.
- Add traversal/normalize/recursion unit tests, stash self-eviction +
  doc-put-throw + empty/octet-stream mock tests, controller If-None-Match
  (wildcard/weak/list) + Cache-Control tests, and SANDBOX_TTL_MS validation
  tests. Regenerate packages/mcp/build.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/server/src/integrations/sandbox/sandbox.controller.ts

@@ -1,6 +1,7 @@
 import { Controller, Get, Param, Req, Res } from '@nestjs/common';
 import { FastifyReply, FastifyRequest } from 'fastify';
 import { SandboxStore } from './sandbox.store';
+import { SANDBOX_ROUTE_SEGMENT } from './sandbox.constants';
 
 // Strict UUID v-agnostic shape. This is anti-traversal / input hygiene (so `:id`
 // can never be a path like `../...`), NOT authorization — the capability is the
@@ -22,7 +23,7 @@ const UUID_RE =
  * UUID; `:id` is never used as a filesystem path, so there is no traversal
  * surface. Never returns tokens, never 401s.
  */
-@Controller('sb')
+@Controller(SANDBOX_ROUTE_SEGMENT)
 export class SandboxController {
   constructor(private readonly store: SandboxStore) {}