fix: WebSearch providers + MCPTool bugs (#593)

* fix: WebSearch providers + MCPTool bugs

WebSearchTool:
- custom.ts: fix buildAuthHeadersForPreset WEB_AUTH_HEADER opt-out
- custom.ts: fix WEB_AUTH_SCHEME empty string handling
- custom.ts: fix walkJsonPath null safety for jsonPath parsing
- duckduckgo.ts: use SafeSearchType enum instead of raw 0
- mojeek.ts: always send Accept: application/json header
- README: fix timeout documentation (15s -> 120s to match code)
- custom.test.ts: add tests for auth header behavior

MCPTool:
- MCPTool.ts: fix outputSchema to accept ContentBlockParam[] (not just string)
- MCPTool.ts: fix isResultTruncated for array output (iterates text blocks)

* fix: address PR #593 review feedback

1. Export buildAuthHeadersForPreset and add direct tests for:
   - WEB_AUTH_HEADER="" explicit opt-out behavior
   - WEB_AUTH_SCHEME="" stripping scheme prefix
   - Preset defaults (authHeader + authScheme)
   - No WEB_KEY returns empty headers

2. Add duckduckgo.test.ts verifying SafeSearchType.STRICT === 0,
   confirming the enum change is semantically identical to the
   previous raw value.

Addresses review by @Vasanthdev2004 at
pullrequestreview-4093533095

---------

Co-authored-by: FluxLuFFy <flux@openclaude.dev>
Co-authored-by: Fix Bot <fix@openclaude.local>

src/tools/WebSearchTool/providers/mojeek.ts

@@ -21,9 +21,10 @@ export const mojeekProvider: SearchProvider = {
     url.searchParams.set('q', input.query)
     url.searchParams.set('fmt', 'json')
 
-    const headers: Record<string, string> = {}
+    const headers: Record<string, string> = {
+      'Accept': 'application/json',
+    }
     if (process.env.MOJEEK_API_KEY) {
-      headers['Accept'] = 'application/json'
       headers['Authorization'] = `Bearer ${process.env.MOJEEK_API_KEY}`
     }