refactor: split 6 oversized packages into semantic subpackages

Structure debt list is now empty (FOLDER_DEBT = Set.of()), every folder
holds at most 4 java files:

- elytra/{mode,generator} -> elytra/core plus per-mode slices (close,
  minspeed, obstacle, speeddemon, timetrial), 2 files each
- command/schematic -> command/schematic (4) + wand/ (2)
- generator/jump: JumpType -> jump/model/, SchematicBlockPlacer ->
  jump/placement/schematic/
- player/core -> player/core (4) + PlayerSpawnSetup -> player/service (4)

18 files moved, imports/tests updated, 5 classes widened to public for
cross-package calls. No behavior change; check and build stay green.

src/test/java/dev/loki/loparkour/arch/StructureRulesTest.java

@@ -25,13 +25,7 @@ class StructureRulesTest {
     private static final int MAX_LINES_PER_FILE = 200;
 
     /** Known debt (docs/TODO.md, task 2). Remove entries as folders get split. */
-    private static final Set<String> FOLDER_DEBT = Set.of(
-            "dev/loki/loparkour/command/schematic",
-            "dev/loki/loparkour/elytra/generator",
-            "dev/loki/loparkour/elytra/mode",
-            "dev/loki/loparkour/generator/jump/calculation",
-            "dev/loki/loparkour/generator/jump/placement",
-            "dev/loki/loparkour/player/core");
+    private static final Set<String> FOLDER_DEBT = Set.of();
 
     @Test
     void foldersHaveAtMostFourFiles() throws IOException {