Add dual-model support with separate chat and agent models

Split the single model setting into `chatModel` and `agentModel` to allow
using different LLMs for conversational modes (Ask, Research) versus
agentic modes (Edit, Organize, Workflow, auto-organizer). Defaults are
`deepseek-v4-flash` for chat and `glm-5.1` for agents.

Includes backward compatibility migration from legacy `model` field,
updated settings UI, per-mode tool filtering via new `agent-modes.ts`
configs, and vault search scoring improvements (exact phrase, recency,
filename bonuses).

tests/chat-view.test.ts

@@ -33,6 +33,8 @@ jest.mock('obsidian', () => ({
 
 const mockSettings: PluginSettings = {
   ollamaUrl: 'http://localhost:11434',
+  chatModel: 'llama3',
+  agentModel: 'llama3',
   model: 'llama3',
   vaultSearchLimit: 3,
   maxMessageHistory: 50,