Offline registry search provider not implemented

## Recommendation

### 🔧 FINISH: Add offline/cached search provider for registry

The registry search gateway has Algolia and ComfyRegistry providers but no offline/cached fallback.

## What Was Found

- `src/services/gateway/registrySearchGateway.ts:57` — `// TODO: Add an "offline" provider that operates on a local cache of the registry.`

## Context

Users without network access cannot search the node registry. An offline provider using a local cache would improve the experience.

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**Category:** Half-Implemented | **Confidence:** MEDIUM | **Tools:** Semantic analysis
_Filed by audit-code skill_

Part of #11022

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-11055-Offline-registry-search-provider-not-implemented-33e6d73d365081da814ce35c26208773) by [Unito](https://www.unito.io)

Start with src/services/gateway/registrySearchGateway.ts around line 57, then read the existing Algolia and ComfyRegistry providers to understand the gateway contract. Determine where the local registry cache is exposed and how offline searches should use it; done means registry searches work without network access through the cached provider.

Written by the indexing model from the issue text.