feat: per-agent model routing — route different agents to different providers (#238)

* feat: add agentModels and agentRouting to SettingsSchema

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: add agentRouting module for per-agent provider resolution

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: thread providerOverride through OpenAI shim for per-agent routing

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: getAnthropicClient accepts providerOverride for agent routing

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: thread providerOverride through Options and queryModel calls

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: thread providerOverride through query loop and ToolUseContext

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: resolve agent routing in runAgent and inject providerOverride

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* docs: add Agent Routing configuration guide to README

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* test: add unit tests for resolveAgentProvider + plaintext api_key note

- 15 tests covering priority chain (name > subagentType > default > null)
- normalize() case-insensitive and hyphen/underscore equivalence
- Edge cases: null settings, missing config sections, non-existent model
- README note about api_key stored in plaintext

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* security: address code review — SSRF, credential leak, key collision

- base_url schema now uses z.string().url() for SSRF mitigation
- Strip auth headers (Authorization, x-api-key, api-key) from
  defaultHeaders when providerOverride is active, preventing
  Anthropic credentials from leaking to third-party endpoints
- Warn on duplicate normalized routing keys to prevent silent shadowing
- providerOverride.apiKey is never logged (verified via grep)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: 冯俊辉 <fengjunhui@shiyanjia.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/tools/AgentTool/AgentTool.tsx

@@ -644,7 +644,8 @@ export const AgentTool = buildTool({
         useExactTools: true
       }),
       worktreePath: worktreeInfo?.worktreePath,
-      description
+      description,
+      agentName: name,
     };
 
     // Helper to wrap execution with a cwd override: explicit cwd arg (KAIROS)