chore(housekeeping): canonical git.d-ma.be host + honest version string

- Dockerfile: GOPRIVATE and the http→https insteadOf rewrite now name
  git.d-ma.be (was the pre-rename gitea.d-ma.be; masked at build time only by
  GOPROXY=direct + GOSUMDB=off).
- .context/PROJECT.md Repo URL → git.d-ma.be, adapters regenerated
  (CLAUDE.md, AGENTS.md, .cursorrules, .aider.conventions.md, system-prompt.txt).
- main.go: version is now a `-ldflags -X main.version` overridable var defaulting
  to "dev" instead of a hardcoded, drifting "0.1.0".

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.context/system-prompt.txt

@@ -293,7 +293,7 @@ Shared engineering skills are available in `~/dev/.skills/`. Load at task start
 - **Name**: gitea-mcp
 - **Owner**: Mathias
 - **Client**: personal
-- **Repo**: https://gitea.d-ma.be/mathias/gitea-mcp
+- **Repo**: https://git.d-ma.be/mathias/gitea-mcp
 - **Status**: active
 
 ## Stack