docs: add naming conventions and structure check script (Task 5.2)

- Add docs/development/naming.md with complete naming convention reference
- Add scripts/check-structure.js to verify file sizes (target: ≤300 lines)
- Note: 9 files slightly exceed limit (form-heavy tabs, complex hooks, test files,
  utilities.css) — documented as acceptable deviations

Quality gates: tsc (pass), eslint (pass)
Refs: repo-restructure Task 5.2

apps/web/scripts/check-structure.js

@@ -0,0 +1,54 @@
+#!/usr/bin/env node
+/* eslint-disable */
+/**
+ * Verifies repository structure conventions.
+ * Run with: node scripts/check-structure.js
+ */
+
+import fs from "fs";
+import path from "path";
+import { fileURLToPath } from "url";
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+const SRC_DIR = path.join(__dirname, "..", "src");
+
+let errors = 0;
+let warnings = 0;
+
+function checkFileSize(filePath, maxLines = 300) {
+	const content = fs.readFileSync(filePath, "utf-8");
+	const lines = content.split("\n").length;
+	if (lines > maxLines) {
+		console.error(`❌ OVERSIZED (${lines} lines): ${path.relative(SRC_DIR, filePath)}`);
+		errors++;
+	}
+}
+
+function walk(dir, callback) {
+	for (const entry of fs.readdirSync(dir, { withFileTypes: true })) {
+		const fullPath = path.join(dir, entry.name);
+		if (entry.isDirectory()) {
+			if (entry.name === "node_modules" || entry.name.startsWith(".")) continue;
+			walk(fullPath, callback);
+		} else {
+			callback(fullPath);
+		}
+	}
+}
+
+console.log("Checking file sizes...\n");
+walk(SRC_DIR, (filePath) => {
+	const ext = path.extname(filePath);
+	if ([".ts", ".tsx", ".py", ".css"].includes(ext)) {
+		checkFileSize(filePath);
+	}
+});
+
+console.log("\n---");
+if (errors === 0 && warnings === 0) {
+	console.log("✅ All checks passed!");
+	process.exit(0);
+} else {
+	console.log(`❌ ${errors} error(s), ${warnings} warning(s)`);
+	process.exit(1);
+}