Add #rss command family with LLM tags and summaries (v0.20.0)

#rss subcommands on the command channel: help / add <url> <name> /
remove <name> / tags / sources / get <name|#tag>. Sources are stored in
a new rss_sources table in the existing MESH_DB_PATH file (second
node:sqlite connection, case-insensitive names); feeds parsed with
fast-xml-parser (RSS 2.0 + Atom); AI tags and headline summaries via
injected LlmService.chat() with bounded maxTokens (50/200).

CommandService gains prefix registration so one handler owns the whole
#rss family while #ping stays an exact match; wired in CommandModule's
factory — still no constructor-level cycle, no forwardRef. One dead feed
does not sink a tag summary.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "mesh-bot",
-  "version": "0.19.0",
+  "version": "0.20.0",
   "description": "",
   "author": "",
   "private": true,
@@ -30,6 +30,7 @@
     "@nestjs/schedule": "^12.0.2",
     "@nestjs/swagger": "^12.0.2",
     "@scalar/nestjs-api-reference": "^1.2.21",
+    "fast-xml-parser": "^5.11.1",
     "reflect-metadata": "^0.2.2",
     "rxjs": "^7.8.1"
   },