docs: create agent.md and CONTEXT.md with full project structure

- Add agent.md for high-level project overview and feature list
- Add CONTEXT.md for detailed development guide and logic explanation
- Refactor project structure: move config.js to constants.js and update references
- Improve camera tracking logic with Lerp and jittering prevention
- Update ArenaScene to support intelligent combat observation and minimap viewport
- Fine-tune combat mechanics: optimize projectile spawn points and hit detection

src/ui/matchForm.js

@@ -1,4 +1,4 @@
-const nicknameLength = 18;
+import { NICKNAME_LENGTH } from "../constants.js";
 
 export function createMatchForm() {
   const form = getElement("#fighter-form");
@@ -46,7 +46,7 @@ function getElement(selector) {
 function nicknameValues(value) {
   return value
     .split(/\r?\n|,/)
-    .map((name) => name.trim().slice(0, nicknameLength))
+    .map((name) => name.trim().slice(0, NICKNAME_LENGTH))
     .filter(Boolean);
 }