Add configurable log levels and log file support

- New LogLevel type: Debug, Info, Warn, Error with Ord instance
- Logger holds configured level and output handle (stderr or file)
- --log-level and --log-file CLI flags
- log_level and log_file YAML config fields
- Log messages assigned appropriate severity levels
- Test logger updated to new Logger structure
- All 17 tests passing

app/Main.hs

@@ -3,6 +3,7 @@ module Main (main) where
 import Converge
 import Data.Maybe (fromMaybe)
 import Data.Text (Text)
+import qualified Data.Text as T
 import Options.Applicative
 import System.IO (hPutStrLn, stderr)
 
@@ -17,6 +18,10 @@ data CliArgs = CliArgs
     -- ^ Branch name (used only in single-repo mode).
     , cliDebounce :: !(Maybe Int)
     -- ^ Debounce override for both modes.
+    , cliLogLevel :: !(Maybe LogLevel)
+    -- ^ Log level override.
+    , cliLogFile :: !(Maybe FilePath)
+    -- ^ Log file path.
     }
 
 cliParser :: Parser CliArgs
@@ -62,6 +67,26 @@ cliParser =
                     <> help "Debounce window in milliseconds (overrides config file)"
                 )
             )
+        <*> optional
+            ( option
+                (maybeReader (\s -> case T.toLower (T.pack s) of
+                    "debug" -> Just Debug
+                    "info"  -> Just Info
+                    "warn"  -> Just Warn
+                    "error" -> Just Error
+                    _       -> Nothing))
+                ( long "log-level"
+                    <> metavar "LEVEL"
+                    <> help "Minimum log level: debug, info, warn, or error (default: info)"
+                )
+            )
+        <*> optional
+            ( strOption
+                ( long "log-file"
+                    <> metavar "FILE"
+                    <> help "Write logs to a file instead of stderr"
+                )
+            )
 
 parserInfo :: ParserInfo CliArgs
 parserInfo =
@@ -79,7 +104,7 @@ main = do
     (options, configSource) <- case cliConfig cli of
         Just cfgPath -> do
             cfg <- loadConfig cfgPath
-            let opts = applyDebounce mDebounceOverride (configToOptions cfg)
+            let opts = applyOverrides mDebounceOverride (cliLogLevel cli) (cliLogFile cli) (configToOptions cfg)
             pure (opts, Just cfgPath)
         Nothing -> do
             exists <- configFileExists
@@ -87,20 +112,21 @@ main = do
                 then do
                     cfgPath <- defaultConfigPath
                     cfg <- loadConfig cfgPath
-                    let opts = applyDebounce mDebounceOverride (configToOptions cfg)
+                    let opts = applyOverrides mDebounceOverride (cliLogLevel cli) (cliLogFile cli) (configToOptions cfg)
                     pure (opts, Just cfgPath)
                 else
                     pure
-                        ( defaultOptions
-                            { optRepos =
-                                [ defaultRepoConfig
-                                    { rcPath = fromMaybe "." (cliRepo cli)
-                                    , rcRemote = cliRemote cli
-                                    , rcBranch = cliBranch cli
-                                    }
-                                ]
-                            , optDebounceMs = fromMaybe 5000 mDebounceOverride
-                            }
+                        ( applyOverrides mDebounceOverride (cliLogLevel cli) (cliLogFile cli)
+                            defaultOptions
+                                { optRepos =
+                                    [ defaultRepoConfig
+                                        { rcPath = fromMaybe "." (cliRepo cli)
+                                        , rcRemote = cliRemote cli
+                                        , rcBranch = cliBranch cli
+                                        }
+                                    ]
+                                , optDebounceMs = fromMaybe 5000 mDebounceOverride
+                                }
                         , Nothing
                         )
     case configSource of
@@ -118,6 +144,14 @@ main = do
     mapM_ (\r -> hPutStrLn stderr ("  - " <> rcPath r)) (optRepos options)
     runConverge options
 
-applyDebounce :: Maybe Int -> Options -> Options
-applyDebounce (Just ms) opts = opts{optDebounceMs = ms}
-applyDebounce Nothing opts = opts
+
+-- | Apply CLI overrides (debounce, log level, log file) to Options.
+applyOverrides :: Maybe Int -> Maybe LogLevel -> Maybe FilePath -> Options -> Options
+applyOverrides mDebounce mLogLevel mLogFile opts =
+    opts
+        { optDebounceMs = maybe (optDebounceMs opts) id mDebounce
+        , optLogLevel = fromMaybe (optLogLevel opts) mLogLevel
+        , optLogFile = case mLogFile of
+            Just _ -> mLogFile  -- CLI --log-file overrides config
+            Nothing -> optLogFile opts
+        }