refactor: consolidate blockchain explorer into single app and update backup ignore patterns

- Remove standalone explorer-web app (README, HTML, package files)
- Add /web endpoint to blockchain-explorer for web interface access
- Update .gitignore to exclude application backup archives (*.tar.gz, *.zip)
- Add backup documentation files to .gitignore (BACKUP_INDEX.md, README.md)
- Consolidate explorer functionality into main blockchain-explorer application

apps/wallet/src/app/security.py

@@ -0,0 +1,43 @@
+from __future__ import annotations
+
+import re
+import threading
+import time
+from collections import defaultdict, deque
+
+
+class RateLimiter:
+    def __init__(self, max_requests: int = 30, window_seconds: int = 60) -> None:
+        self._max_requests = max_requests
+        self._window_seconds = window_seconds
+        self._lock = threading.Lock()
+        self._records: dict[str, deque[float]] = defaultdict(deque)
+
+    def allow(self, key: str) -> bool:
+        now = time.monotonic()
+        with self._lock:
+            entries = self._records[key]
+            while entries and now - entries[0] > self._window_seconds:
+                entries.popleft()
+            if len(entries) >= self._max_requests:
+                return False
+            entries.append(now)
+            return True
+
+
+def validate_password_rules(password: str) -> None:
+    if len(password) < 12:
+        raise ValueError("password must be at least 12 characters long")
+    if not re.search(r"[A-Z]", password):
+        raise ValueError("password must include at least one uppercase letter")
+    if not re.search(r"[a-z]", password):
+        raise ValueError("password must include at least one lowercase letter")
+    if not re.search(r"\d", password):
+        raise ValueError("password must include at least one digit")
+    if not re.search(r"[^A-Za-z0-9]", password):
+        raise ValueError("password must include at least one symbol")
+
+
+def wipe_buffer(buffer: bytearray) -> None:
+    for index in range(len(buffer)):
+        buffer[index] = 0