fix(02): revise plans based on checker feedback

- 02-01 Task 3: Add concrete REPL verification command for PluginManifest.parse
- 02-02 Task 1: Add FieldDef case class to placeholder types in PluginRegistration.scala
- 02-02 Task 1: Document PluginEnv as placeholder to be expanded in 02-03
- 02-03 Task 3: Remove duplicate Main.scala code, keep only corrected version
- 02-03: Add SummerPlugin.scala to files_modified for PluginEnv update

.planning/phases/02-plugin-system/02-02-PLAN.md

@@ -136,7 +136,9 @@ case class PluginRegistration(
   // Event subscriptions (Phase 2 extension API)
   events: List[EventSubscription] = List.empty,
   // Extensions to other plugins (Phase 2 extension API)
-  extensions: List[ExtensionDef] = List.empty
+  extensions: List[ExtensionDef] = List.empty,
+  // Form field definitions (for YAML-driven forms)
+  fields: List[FieldDef] = List.empty
 )
 
 object PluginRegistration:
@@ -149,6 +151,7 @@ case class NavigationDef(id: String, label: String, url: String, icon: String =
 case class SettingDef(key: String, label: String, icon: String = "")
 case class EventSubscription(eventType: String, handler: String)
 case class ExtensionDef(target: String, extensionClass: String)
+case class FieldDef(name: String, fieldType: String)
 ```
 
 **SummerPlugin.scala:**
@@ -172,6 +175,9 @@ trait SummerPlugin:
    * Async boot phase - can perform effects.
    * Called after all dependencies have booted.
    * Use for: database setup, event subscriptions, service initialization.
+   *
+   * PluginEnv is a placeholder that will be expanded in 02-03 to include
+   * EventService and ExtensionRegistry when the extension API is implemented.
    */
   def boot: ZIO[PluginEnv, PluginError, Unit] = ZIO.unit
 
@@ -181,12 +187,15 @@ trait SummerPlugin:
    */
   def shutdown: ZIO[Any, Nothing, Unit] = ZIO.unit
 
-/** Environment available to plugins during boot */
+/**
+ * Environment available to plugins during boot.
+ * Initially just PluginContext; extended in 02-03 to include EventService & ExtensionRegistry.
+ */
 type PluginEnv = PluginContext
 ```
   </action>
   <verify>Run `./mill summercms.compile` - all types compile without errors</verify>
-  <done>PluginState enum with all lifecycle states, PluginContext, PluginRegistration with placeholder defs, SummerPlugin trait</done>
+  <done>PluginState enum with all lifecycle states, PluginContext, PluginRegistration with placeholder defs including FieldDef, SummerPlugin trait</done>
 </task>
 
 <task type="auto">