feat(search): add ollama-search and zai-search with credential fallback

Register two web search providers that reuse an existing chat provider's
API key instead of requiring their own connection:

- ollama-search (POST ollama.com/api/web_search) reuses the `ollama` key
- zai-search (POST api.z.ai MCP web_search_prime) reuses the `glm` key

A new `credentialFallback` registry field drives this: when a search
provider has no connection of its own, the search handler falls back to
the linked chat provider's credentials.

Also teach getProviderIconSrc to serve .svg logos for providers that
ship vector art.

open-sse/providers/registry/ollama-search.js

@@ -0,0 +1,35 @@
+export default {
+  id: "ollama-search",
+  alias: "ollama-search",
+  display: {
+    name: "Ollama Search",
+    icon: "cloud",
+    color: "#ffffff",
+    textIcon: "OL",
+    website: "https://ollama.com",
+    notice: {
+      text: "Web search via Ollama Cloud subscription. Reuses the API key from the Ollama (chat) provider.",
+      apiKeyUrl: "https://ollama.com/settings/keys",
+    },
+  },
+  category: "apikey",
+  authType: "apikey",
+  authModes: ["apikey"],
+  serviceKinds: ["webSearch"],
+  // Credential fallback: reuses the API key registered under the `ollama`
+  // chat provider — one key, chat + search.
+  credentialFallback: "ollama",
+  searchConfig: {
+    baseUrl: "https://ollama.com/api/web_search",
+    method: "POST",
+    authType: "apikey",
+    authHeader: "bearer",
+    costPerQuery: 0,
+    freeMonthlyQuota: 1000,
+    searchTypes: ["web"],
+    defaultMaxResults: 5,
+    maxMaxResults: 10,
+    timeoutMs: 10000,
+    cacheTTLMs: 300000,
+  },
+};