fix: improve CloudSigma error messages and update RamNode README (#947)

CloudSigma UX fixes:
- Use log_error consistently for remediation hints (was log_warn)
- Add "Common issues" block to create_server failure
- Add actionable hints to server timeout error
- Extract API error message instead of dumping raw response
- Fix README: VNC password is random, not hardcoded

RamNode README:
- Update implemented agents list from 9 to all 15

Agent: ux-engineer

Co-authored-by: A <6723574+louisgv@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ramnode/README.md

@@ -149,13 +149,19 @@ Uses OpenStack Compute API:
 
 - ✅ Claude Code
 - ✅ Aider
-- ✅ Goose
-- ✅ Open Interpreter
-- ✅ NanoClaw
-- ✅ OpenClaw
+- ✅ Amazon Q
 - ✅ Cline
-- ✅ gptme
+- ✅ Codex
 - ✅ Continue
+- ✅ Gemini CLI
+- ✅ Goose
+- ✅ gptme
+- ✅ Kilocode
+- ✅ NanoClaw
+- ✅ Open Interpreter
+- ✅ OpenClaw
+- ✅ OpenCode
+- ✅ Plandex
 
 ## Documentation