feat: add Brave Web Search WASM tool (#474)

* feat: add Brave Web Search WASM tool

Add a new WASM tool for searching the web via the Brave Search API.
Follows the same architecture as the GitHub WASM tool with zero-exposure
credential injection (X-Subscription-Token header).

Features:
- Full Brave Search API support (query, count, country, search_lang,
  ui_lang, freshness)
- Input validation on all parameters
- Retry logic for 429/5xx transient errors
- RFC 3986 percent-encoding
- Registry manifest for Extensions tab discovery

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

* fix: avoid Vec allocation in is_valid_ui_lang

Use iterator-based destructuring instead of collecting into a Vec,
avoiding a heap allocation in the WASM sandbox.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <[email protected]>

registry/tools/web-search.json

@@ -0,0 +1,31 @@
+{
+  "name": "web-search",
+  "display_name": "Web Search",
+  "kind": "tool",
+  "version": "0.1.0",
+  "description": "Search the web using Brave Search API",
+  "keywords": ["search", "web", "brave", "internet"],
+
+  "source": {
+    "dir": "tools-src/web-search",
+    "capabilities": "web-search-tool.capabilities.json",
+    "crate_name": "web-search-tool"
+  },
+
+  "artifacts": {
+    "wasm32-wasip2": {
+      "url": "https://github.com/nearai/ironclaw/releases/latest/download/web-search-wasm32-wasip2.tar.gz",
+      "sha256": null
+    }
+  },
+
+  "auth_summary": {
+    "method": "manual",
+    "provider": "Brave",
+    "secrets": ["brave_api_key"],
+    "shared_auth": null,
+    "setup_url": "https://brave.com/search/api/"
+  },
+
+  "tags": ["default", "search"]
+}