feat: add multi-server support

Connect to multiple IRC servers concurrently from a single config file.
Plugins are loaded once and shared; per-server state is isolated via
separate SQLite databases and per-bot runtime state (bot._pstate).

- Add build_server_configs() for [servers.*] config layout
- Bot.__init__ gains name parameter, _pstate dict for plugin isolation
- cli.py runs multiple bots via asyncio.gather
- 9 stateful plugins migrated from module-level dicts to _ps(bot) pattern
- Backward compatible: legacy [server] config works unchanged

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

plugins/urltitle.py

@@ -38,9 +38,14 @@ _SKIP_EXTS = frozenset({
 # Trailing punctuation to strip, but preserve balanced parens
 _TRAIL_CHARS = set(".,;:!?)>]")
 
-# -- Module-level state ------------------------------------------------------
+# -- Per-bot state -----------------------------------------------------------
 
-_seen: dict[str, float] = {}
+
+def _ps(bot):
+    """Per-bot plugin runtime state."""
+    return bot._pstate.setdefault("urltitle", {
+        "seen": {},
+    })
 
 # -- HTML parser -------------------------------------------------------------
 
@@ -202,21 +207,22 @@ def _fetch_title(url: str) -> tuple[str, str]:
 # -- Cooldown ----------------------------------------------------------------
 
 
-def _check_cooldown(url: str, cooldown: int) -> bool:
+def _check_cooldown(bot, url: str, cooldown: int) -> bool:
     """Return True if the URL is within the cooldown window."""
+    seen = _ps(bot)["seen"]
     now = time.monotonic()
-    last = _seen.get(url)
+    last = seen.get(url)
     if last is not None and (now - last) < cooldown:
         return True
 
     # Prune if cache is too large
-    if len(_seen) >= _CACHE_MAX:
+    if len(seen) >= _CACHE_MAX:
         cutoff = now - cooldown
-        stale = [k for k, v in _seen.items() if v < cutoff]
+        stale = [k for k, v in seen.items() if v < cutoff]
         for k in stale:
-            del _seen[k]
+            del seen[k]
 
-    _seen[url] = now
+    seen[url] = now
     return False
 
 
@@ -261,7 +267,7 @@ async def on_privmsg(bot, message):
     for url in urls:
         if _is_ignored_url(url, ignore_hosts):
             continue
-        if _check_cooldown(url, cooldown):
+        if _check_cooldown(bot, url, cooldown):
             continue
 
         title, desc = await loop.run_in_executor(None, _fetch_title, url)