dashboard: add keyboard shortcuts and optimize polling

- fetch.py: convert proxy validation cache to LRU with OrderedDict
  - thread-safe lock, move_to_end() on hits, evict oldest when full
- dashboard.js: add keyboard shortcuts (r=refresh, 1-9=tabs, t=theme, p=pause)
- dashboard.js: skip chart rendering for inactive tabs (reduces CPU)

fetch.py

@@ -1,6 +1,7 @@
 import re, random, time, string
 import json
 import threading
+from collections import OrderedDict
 import rocksock
 import network_stats
 from http2 import RsHttp, _parse_url
@@ -9,9 +10,11 @@ from misc import _log, tor_proxy_url
 
 config = None
 
-# Cache for is_usable_proxy() - avoids repeated validation of same proxy strings
-_proxy_valid_cache = {}
+# LRU cache for is_usable_proxy() - avoids repeated validation of same proxy strings
+# Uses OrderedDict to maintain insertion order; oldest entries evicted when full
+_proxy_valid_cache = OrderedDict()
 _proxy_valid_cache_max = 10000
+_proxy_valid_cache_lock = threading.Lock()
 
 
 class FetchSession(object):
@@ -603,16 +606,20 @@ def is_usable_proxy(proxy):
     - Invalid port (0, >65535)
     - Private/reserved ranges
 
-    Results are cached to avoid repeated validation of the same proxy strings.
+    Results are cached using LRU eviction to avoid repeated validation.
     """
-    # Check cache first
-    if proxy in _proxy_valid_cache:
-        return _proxy_valid_cache[proxy]
+    with _proxy_valid_cache_lock:
+        if proxy in _proxy_valid_cache:
+            # Move to end (most recently used)
+            _proxy_valid_cache.move_to_end(proxy)
+            return _proxy_valid_cache[proxy]
 
     result = _validate_proxy(proxy)
 
-    # Cache result (with size limit)
-    if len(_proxy_valid_cache) < _proxy_valid_cache_max:
+    with _proxy_valid_cache_lock:
+        # Evict oldest entries if at capacity
+        while len(_proxy_valid_cache) >= _proxy_valid_cache_max:
+            _proxy_valid_cache.popitem(last=False)
         _proxy_valid_cache[proxy] = result
 
     return result