feat(knowledge): 任务队列、独立 worker 与 pgvector 向量索引

知识处理改为数据库任务队列，独立 worker 做切块与向量化，失败可重试。

backend/app/knowledge/domains.py

@@ -0,0 +1,56 @@
+"""
+Copyright 2024-2026 ChatterMate
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+
+Single canonical registrable-domain helper, used everywhere a sub-page URL is
+compared against its source's domain (website crawler, sitemap parser, manual
+add-subpage). Same-domain enforcement stops one plan-limited knowledge source
+from accumulating content across unrelated domains. Handles common ccTLDs
+(co.uk, com.au, …) so 'a.example.co.uk' → 'example.co.uk' rather than 'co.uk'
+(the latter would wrongly treat every *.co.uk host as one domain).
+"""
+
+from urllib.parse import urlparse
+
+# Second-level labels that sit under a 2-letter ccTLD (best-effort; a full
+# public-suffix list would be a heavy dependency for marginal gain here).
+_CCTLD_SECOND_LEVELS = frozenset(
+    {"co", "com", "org", "net", "edu", "gov", "ac", "gov", "ltd", "plc", "me", "or", "ne"}
+)
+
+
+def registrable_domain(host: str) -> str:
+    """Registrable domain for a HOST (not a full URL): lowercased, port/userinfo
+    already stripped by the caller's urlparse(...).hostname, 'www.' removed."""
+    host = (host or "").lower().strip().rstrip(".")
+    if host.startswith("www."):
+        host = host[4:]
+    if not host:
+        return ""
+    parts = host.split(".")
+    if len(parts) > 2 and parts[-2] in _CCTLD_SECOND_LEVELS and len(parts[-1]) == 2:
+        return ".".join(parts[-3:])
+    return ".".join(parts[-2:]) if len(parts) > 1 else host
+
+
+def domain_of_url(url: str) -> str:
+    """Registrable domain of a URL string. A scheme-less value ('example.com/x')
+    is normalized so its host is still recognised (else it would parse as a
+    path with no hostname and silently bypass a same-domain check)."""
+    text = (url or "").strip()
+    if not text:
+        return ""
+    if "://" not in text:
+        text = f"https://{text}"
+    return registrable_domain(urlparse(text).hostname or "")