Add task complexity field and model selection

Add complexity-based model selection:

Task Model Changes

Add to Task in Core.hs: taskComplexity :: Maybe Int -- 1-5 scale

Update:

• SQL schema (ALTER TABLE or migration)
• FromRow/ToRow instances
• createTask to accept complexity
• JSON instances

CLI Changes

jr task create --complexity=3 'Task title' jr task edit t-xxx --complexity=4

Model Selection in Worker (OpenRouter + Claude)

selectModel :: Maybe Int -> Text selectModel Nothing = "anthropic/claude-sonnet-4-20250514" -- Default selectModel (Just 1) = "anthropic/claude-haiku" -- Trivial selectModel (Just 2) = "anthropic/claude-haiku" -- Low selectModel (Just 3) = "anthropic/claude-sonnet-4-20250514" -- Medium selectModel (Just 4) = "anthropic/claude-sonnet-4-20250514" -- High selectModel (Just 5) = "anthropic/claude-opus-4-20250514" -- Expert

Web UI (Optional, could be separate task)

• Show complexity on task detail
• Dropdown to change complexity