docs: add missing skills, CLI commands, and messaging env vars

Complete the documentation gaps identified in the previous audit:

Skills catalogs:
- skills-catalog.md: Add 7 missing bundled skills — data-science/
  jupyter-live-kernel, dogfood/hermes-agent-setup, inference-sh/
  inference-sh-cli, mlops/huggingface-hub, productivity/linear,
  research/parallel-cli, social-media/xitter
- optional-skills-catalog.md: Add 8 missing optional skills —
  blockchain/base, creative/blender-mcp, creative/meme-generation,
  mcp/fastmcp, productivity/telephony, research/bioinformatics,
  security/oss-forensics, security/sherlock

CLI commands reference:
- cli-commands.md: Add full documentation for hermes mcp (add/remove/
  list/test/configure) and hermes plugins (install/update/remove/list)

Messaging platform docs:
- discord.md: Add DISCORD_REQUIRE_MENTION and
  DISCORD_FREE_RESPONSE_CHANNELS to manual config env vars section
- signal.md: Add SIGNAL_ALLOW_ALL_USERS to env var reference table
- slack.md: Add SLACK_HOME_CHANNEL_NAME to config section

website/docs/user-guide/messaging/signal.md

@@ -234,4 +234,5 @@ The adapter monitors the SSE connection and automatically reconnects if:
 | `SIGNAL_ACCOUNT` | Yes | — | Bot phone number (E.164) |
 | `SIGNAL_ALLOWED_USERS` | No | — | Comma-separated phone numbers/UUIDs |
 | `SIGNAL_GROUP_ALLOWED_USERS` | No | — | Group IDs to monitor, or `*` for all (omit to disable groups) |
+| `SIGNAL_ALLOW_ALL_USERS` | No | `false` | Allow any user to interact (skip allowlist) |
 | `SIGNAL_HOME_CHANNEL` | No | — | Default delivery target for cron jobs |