Add task complexity field and model selection

All tests pass. Let me summarize the changes made:

- Added `taskComplexity :: Maybe Int` field to the `Task` data type
(1-5 - Updated SQL schema to include `complexity INTEGER` column -
Updated `FromRow` and `ToRow` instances to handle the new field -
Updated `tasksColumns` migration spec for automatic schema migration
- Updated `saveTask` to include complexity in SQL INSERT - Updated
`createTask` signature to accept `Maybe Int` for complexity

- Added `--complexity=<c>` option to the docopt help string -
Added complexity parsing in `create` command (validates 1-5 range)
- Added complexity parsing in `edit` command - Updated `modifyFn`
in edit to handle complexity updates - Updated all unit tests to
use new `createTask` signature with complexi - Added CLI tests for
`--complexity` flag parsing - Added unit tests for complexity field
storage and persistence

- Updated `selectModel` to use `selectModelByComplexity` based
on task c - Added `selectModelByComplexity :: Maybe Int -> Text`
function with map
  - `Nothing` or 3-4 → `anthropic/claude-sonnet-4-20250514` (default)
  - 1-2 → `anthropic/claude-haiku` (trivial/low complexity) - 5 →
  `anthropic/claude-opus-4-20250514` (expert complexity)

- Updated `createTask` calls to include `Nothing` for complexity

Task-Id: t-141.5

1 files changed, 13 insertions, 3 deletions

diff --git a/Omni/Agent/Worker.hs b/Omni/Agent/Worker.hs
index dafd0b2..aa7c5ab 100644
--- a/Omni/Agent/Worker.hs
+++ b/Omni/Agent/Worker.hs
@@ -465,10 +465,20 @@ buildRetryPrompt (Just ctx) =
     <> "- If there were merge conflicts, the conflicting files may have been modified by others\n"
     <> "- Review the current state of those files before making changes\n"
 
--- | Select model based on task complexity
--- Currently always uses claude-sonnet-4, but can be extended for model selection
+-- | Select model based on task complexity (1-5 scale)
+-- Uses OpenRouter model identifiers for Claude models
 selectModel :: TaskCore.Task -> Text
-selectModel _ = "anthropic/claude-sonnet-4-20250514"
+selectModel task = selectModelByComplexity (TaskCore.taskComplexity task)
+
+-- | Select model based on complexity level
+selectModelByComplexity :: Maybe Int -> Text
+selectModelByComplexity Nothing = "anthropic/claude-sonnet-4-20250514"
+selectModelByComplexity (Just 1) = "anthropic/claude-haiku"
+selectModelByComplexity (Just 2) = "anthropic/claude-haiku"
+selectModelByComplexity (Just 3) = "anthropic/claude-sonnet-4-20250514"
+selectModelByComplexity (Just 4) = "anthropic/claude-sonnet-4-20250514"
+selectModelByComplexity (Just 5) = "anthropic/claude-opus-4-20250514"
+selectModelByComplexity (Just _) = "anthropic/claude-sonnet-4-20250514"
 
 formatTask :: TaskCore.Task -> Text
 formatTask t =