docs: MCP gateway git/gitlab/paper-search; CT 109 plan; new backrest/db/arcane docs

- mcp-gateway.md: 26 servers (added git, gitlab, paper-search catalog bridge);
  document --pass-environment requirement for env var passthrough in DinD bridges
- ct-inventory.md + homelab-architecture.md: CT 109 IP conflict, CT 113 live
- proxmox-state.md §16: Loki, sshwifty, Alloy, IP conflict note, sidecar table
  expanded to CT 103/111/113; build order updated
- infra/portmap.md: CT 113 db section; QNAP TS-251D (Klipper/Mainsail)
- services/backrest.md: full backup strategy doc (new)
- services/databases.md: CT 113 postgres/WAL-G/pgAdmin doc (new)
- services/arcane.md: Docker management IDE doc (new)
- CHANGELOG.md: 2026-05-22 entry

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CHANGELOG.md

@@ -2,6 +2,13 @@
 
 All notable infrastructure / service / doc changes. Newest first.
 
+## 2026-05-22
+
+- **MCP gateway**: added `git`, `gitlab` (DLR, `--pass-environment` fix for mcp-proxy env passthrough bug), `paper-search` (Docker catalog image replaces inline `python:3.12-slim`); `UNPAYWALL_EMAIL` wired into paper-search. Removed duplicate `papersearch` container. Updated `services/mcp-gateway.md`.
+- **CT 109 plan updated**: IP conflict noted (`.6` taken by CT 113); RAM 8 GiB, disk 50 GiB; Loki added; sshwifty added (multi-tab web SSH); Alloy replaces Promtail on all hosts; sidecar table expanded to CT 103/111/113.
+- **Portmap**: CT 113 (`db`, `.6`) section added; QNAP TS-251D (Klipper/Mainsail) section added.
+- **New docs**: `services/backrest.md`, `services/databases.md`, `services/arcane.md`.
+
 ## 2026-05-21
 
 ### Docs & docs infrastructure