t-247: Add Provider abstraction for multi-backend LLM support

- Create Omni/Agent/Provider.hs with unified Provider interface
- Support OpenRouter (cloud), Ollama (local), Amp (subprocess stub)
- Add runAgentWithProvider to Engine.hs for Provider-based execution
- Add EngineType to Core.hs (EngineOpenRouter, EngineOllama, EngineAmp)
- Add --engine flag to 'jr work' command
- Worker.hs dispatches to appropriate provider based on engine type

Usage:
  jr work <task-id>                    # OpenRouter (default)
  jr work <task-id> --engine=ollama    # Local Ollama
  jr work <task-id> --engine=amp       # Amp CLI (stub)

1 files changed, 12 insertions, 3 deletions

diff --git a/Omni/Jr.hs b/Omni/Jr.hs
index b60a029..48dbf90 100755
--- a/Omni/Jr.hs
+++ b/Omni/Jr.hs
@@ -53,7 +53,7 @@ jr
 
 Usage:
   jr task [<args>...]
-  jr work [<task-id>]
+  jr work [<task-id>] [--engine=ENGINE]
   jr prompt <task-id>
   jr web [--port=PORT]
   jr review [<task-id>] [--auto]
@@ -77,6 +77,7 @@ Commands:
 Options:
   -h --help           Show this help
   --port=PORT         Port for web server [default: 8080]
+  --engine=ENGINE     LLM engine: openrouter, ollama, amp [default: openrouter]
   --auto              Auto-review: accept if tests pass, reject if they fail
   --delay=SECONDS     Delay between loop iterations [default: 5]
   --project=PROJECT   Filter facts by project
@@ -119,13 +120,20 @@ move args
       absPath <- Directory.getCurrentDirectory
       let name = Text.pack (takeFileName absPath)
 
+      -- Parse engine flag
+      let engineType = case Cli.getArg args (Cli.longOption "engine") of
+            Just "ollama" -> AgentCore.EngineOllama
+            Just "amp" -> AgentCore.EngineAmp
+            _ -> AgentCore.EngineOpenRouter
+
       let worker =
             AgentCore.Worker
               { AgentCore.workerName = name,
                 AgentCore.workerPid = Nothing,
                 AgentCore.workerStatus = AgentCore.Idle,
                 AgentCore.workerPath = path,
-                AgentCore.workerQuiet = False -- Show ANSI status bar for manual work
+                AgentCore.workerQuiet = False, -- Show ANSI status bar for manual work
+                AgentCore.workerEngine = engineType
               }
 
       let taskId = fmap Text.pack (Cli.getArg args (Cli.argument "task-id"))
@@ -183,7 +191,8 @@ runLoop delaySec = do
                         AgentCore.workerPid = Nothing,
                         AgentCore.workerStatus = AgentCore.Idle,
                         AgentCore.workerPath = ".",
-                        AgentCore.workerQuiet = True -- No ANSI status bar in loop mode
+                        AgentCore.workerQuiet = True, -- No ANSI status bar in loop mode
+                        AgentCore.workerEngine = AgentCore.EngineOpenRouter -- Default for loop
                       }
               putText "[loop] Starting worker..."
               AgentWorker.start worker (Just (TaskCore.taskId task))