feat: add main questline / overarching story system (#24)

- 22 chapters across the full game arc (18 zone bosses + 4 milestones)
- Choice-based narrative with {characterName} dynamic substitution
- Story progress (unlocked + completed chapters) is permanent across all resets
- Server-side anti-cheat: chapters/choices can only accumulate, never be removed
- Tab badge and lower-right toast notifications for newly unlocked chapters
- Story choices displayed on the Character Sheet and Character Page
- How to Play entry added to About panel

apps/api/src/routes/game.ts

@@ -373,7 +373,28 @@ const validateAndSanitize = (incoming: GameState, previous: GameState): GameStat
     };
   })();
 
-  return { ...incoming, resources, bosses, quests, achievements, prestige, ...transcendenceSpread, ...apotheosisSpread, ...explorationSpread };
+  // Story progress: completed chapters can only grow, unlocked IDs can only grow.
+  // Low cheat risk (no rewards), so we allow all incoming additions.
+  const storySpread = (() => {
+    if (!incoming.story) return previous.story ? { story: previous.story } : {};
+    const prevUnlocked = previous.story?.unlockedChapterIds ?? [];
+    const prevCompleted = previous.story?.completedChapters ?? [];
+    // Allow new chapter IDs to be added; never remove existing ones
+    const unlockedChapterIds = [
+      ...prevUnlocked,
+      ...incoming.story.unlockedChapterIds.filter((id) => !prevUnlocked.includes(id)),
+    ];
+    // Allow new completed chapters; never remove existing ones (one entry per chapter)
+    const completedChapters = [
+      ...prevCompleted,
+      ...incoming.story.completedChapters.filter(
+        (c) => !prevCompleted.some((p) => p.chapterId === c.chapterId),
+      ),
+    ];
+    return { story: { unlockedChapterIds, completedChapters } };
+  })();
+
+  return { ...incoming, resources, bosses, quests, achievements, prestige, ...transcendenceSpread, ...apotheosisSpread, ...explorationSpread, ...storySpread };
 };
 
 export const gameRouter = new Hono<HonoEnv>();

apps/api/src/services/apotheosis.ts

@@ -35,6 +35,8 @@ export const buildPostApotheosisState = (
     ...(currentState.codex ? { codex: currentState.codex } : {}),
     // Apotheosis data is eternal — never wiped by any reset
     apotheosis: newApotheosisData,
+    // Story chapter progress is permanent — survives all resets
+    ...(currentState.story ? { story: currentState.story } : {}),
   };
 
   return { newState, newApotheosisData };

apps/api/src/services/prestige.ts

@@ -122,6 +122,8 @@ export const buildPostPrestigeState = (
     ...(currentState.transcendence ? { transcendence: currentState.transcendence } : {}),
     // Apotheosis data is eternal — never wiped by prestige
     ...(currentState.apotheosis ? { apotheosis: currentState.apotheosis } : {}),
+    // Story chapter progress is permanent — survives all resets
+    ...(currentState.story ? { story: currentState.story } : {}),
   };
 
   return { newState, newPrestigeData, runestonesEarned, milestoneRunestones };

apps/api/src/services/transcendence.ts

@@ -80,6 +80,8 @@ export const buildPostTranscendenceState = (
     transcendence: newTranscendenceData,
     // Apotheosis data is eternal — never wiped by transcendence
     ...(currentState.apotheosis ? { apotheosis: currentState.apotheosis } : {}),
+    // Story chapter progress is permanent — survives all resets
+    ...(currentState.story ? { story: currentState.story } : {}),
   };
 
   return { newState, newTranscendenceData, echoesEarned };