chore: sync vendor/zoekt with upstream sourcegraph/zoekt

Bumps the vendor/zoekt submodule to pull in 108 upstream commits from
sourcegraph/zoekt. See sourcebot-dev/zoekt#10.

The -shard_prefix flag on zoekt-git-index was renamed upstream to
-shard_prefix_override; the backend indexer is updated accordingly.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: msukkari

packages/backend/src/zoekt.ts

@@ -23,7 +23,7 @@ export const indexGitRepository = async (repo: Repo, settings: Settings, revisio
         `-branches "${revisions.join(',')}"`,
         `-tenant_id ${repo.orgId}`,
         `-repo_id ${repo.id}`,
-        `-shard_prefix ${shardPrefix}`,
+        `-shard_prefix_override ${shardPrefix}`,
         ...largeFileGlobPatterns.map((pattern) => `-large_file "${pattern}"`),
         repoPath
     ].join(' ');