Add stegasoo info command and update docs for v4.1

- Enhanced `stegasoo info` with fastfetch-style output
  - Service status, URL, channel key, DCT support
  - System stats with --full (CPU, temp, uptime, disk)
- Updated UNDER_THE_HOOD.md for v4.1
  - Added v4.1 changes table (channel keys, docker, Pi wizard)
  - Updated architecture diagram
  - Added channel module to responsibilities

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

PLAN-4.1.4.md

@@ -9,14 +9,14 @@
 ## Features
 - [ ] QR channel key sharing (needs UI thought - avoid crowding encode/decode pages)
 - [ ] Role-based permissions: admin / mod / user
-- [ ] `stegasoo info` fastfetch-style command (version, service status, channel, CPU, temp, etc.)
+- [x] `stegasoo info` fastfetch-style command (version, service status, channel, CPU, temp, etc.)
 - [ ] Better capacity estimates / pre-flight check before encode fails
 
 ## Security
 - [ ] Optional encryption for temp file storage (paranoid mode, config toggle)
 
 ## Docs
-- [ ] Update UNDER_THE_HOOD.md
+- [x] Update UNDER_THE_HOOD.md (v4.1 changes, channel keys)
 - [ ] General docs refresh
 
 ## Ideas (maybe later)