[FEATURE] #880 - Add LearningMode config (off | batch) to settings

[stephanj]

Parent Issue

Part of #880 — Introduce Batch-Level Learning and Strategy Memory

Context

The batch learning feature must be opt-in. A new configuration setting is needed to control whether cross-task learning is active during batch runs. When off (default), behavior is identical to today — each task runs in a fresh, isolated context.

Task

Add a LearningMode setting to the Agent/Spec settings UI.

Key Changes

1. Create LearningMode enum:

   public enum LearningMode {
       OFF,    // default — no cross-task learning
       BATCH   // learning summaries injected into subsequent tasks
   }

2. Add settings fields to the Agent settings UI:

   • Learning mode dropdown (Off / Batch)
   • Max learning context length spinner (default 1500 chars)
   • "Include telemetry in context" checkbox (inject timing/cost data)

3. Persist via DevoxxGenieSettingsService or equivalent state service.

4. Expose so SpecTaskRunnerService and SpecContextBuilder can read the mode.

Files to Create / Modify

• src/main/java/com/devoxx/genie/model/enumarations/LearningMode.java (new)
• src/main/java/com/devoxx/genie/ui/settings/agent/AgentSettingsComponent.java
• src/main/java/com/devoxx/genie/service/DevoxxGenieSettingsService.java

Acceptance Criteria

• LearningMode enum with OFF and BATCH values
• Settings UI exposes mode toggle, max context length, and telemetry checkbox
• Settings persist across IDE restarts
• Default is OFF (backward compatible)