feat(intelligence): add PainAggregator + SolutionGenerator (Chunk 2)

PainAggregator: cross-session pain point merge with confidence scoring,
rule-based frustration detection, and category classification.

SolutionGenerator: transforms high-confidence pain points into proposals
with concrete steps, skill hints, and lifecycle management.

5 Tauri commands registered: butler_list_pain_points, butler_record_pain_point,
butler_generate_solution, butler_list_proposals, butler_update_proposal_status.

desktop/src-tauri/src/intelligence/mod.rs

@@ -32,6 +32,8 @@ pub mod reflection;
 pub mod identity;
 pub mod validation;
 pub mod extraction_adapter;
+pub mod pain_aggregator;
+pub mod solution_generator;
 
 // Re-export main types for convenience
 pub use heartbeat::HeartbeatEngineState;