news digest (spec-013): rss/atom -> {news} file via cron

Replaces the broken pre-1.0-openai news_feed.py. Stdlib parsing with
defusedxml (feeds are untrusted XML), titles sanitized (SAF-03), feed
URLs SSRF-guarded. CLI: python -m fjerkroa_bot.news --config <cfg>.

uv.lock

@@ -627,6 +627,7 @@ version = "3.0.0"
 source = { editable = "." }
 dependencies = [
     { name = "aiohttp" },
+    { name = "defusedxml" },
     { name = "discord-py" },
     { name = "openai" },
     { name = "requests" },
@@ -656,6 +657,7 @@ dev = [
 [package.metadata]
 requires-dist = [
     { name = "aiohttp", specifier = ">=3.12" },
+    { name = "defusedxml", specifier = ">=0.7" },
     { name = "discord-py", specifier = ">=2.5,<3" },
     { name = "openai", specifier = ">=2.45" },
     { name = "requests", specifier = ">=2.32" },