Reorganize code and document functions

lib/repl.mli

@@ -0,0 +1,21 @@
+(** Interactive command loop for the inspector.
+
+    The REPL (Read–Eval–Print Loop) repeatedly reads commands from standard
+    input and applies them to the current navigation state.
+
+    Each command may update the state (for example moving the cursor) or display
+    information about the current log line.
+
+    The loop continues until the user enters ["quit"] or ["exit"], or until an
+    end-of-file condition is encountered on standard input (for example when
+    pressing Ctrl-D). *)
+
+val loop : State.t -> unit
+(** [loop state] starts the interactive command loop.
+
+    The given [state] represents the current navigation state of the loaded log
+    file. Commands executed by the user may derive new states (for example via
+    {!State.next} or {!State.prev}) which are then used in the next iteration of
+    the loop.
+
+    The function runs until the user exits the program. *)