chore(spec-016): mark git-markdown-source done

Refs #31

Author: hendrikebbers

docs/specs/INDEX.md

@@ -21,5 +21,5 @@ roadmap step, to be implemented sequentially (each builds on the previous).
 | 013 | 013-scoped-search-key | Scoped search key | backend, search, security | Read-only scoped Meilisearch key for the content index | #25 | done |
 | 014 | 014-ops-robustness | Ops & robustness | backend, infrastructure, observability | robots.txt handling, fault tolerance, logging/metrics | #27 | done |
 | 015 | 015-additional-web-sources | Additional web sources | backend, configuration | hiero.org/blog + Support & Care as config-only sources | #29 | done |
-| 016 | 016-git-markdown-source | Git markdown source | backend, architecture, security | `type: git` source + `GitSourceStrategy` (GitHub Markdown) | #31 | in progress |
+| 016 | 016-git-markdown-source | Git markdown source | backend, architecture, security | `type: git` source + `GitSourceStrategy` (GitHub Markdown) | #31 | done |
 | 017 | 017-search-enhancements | Search enhancements | backend, search | Facets, synonyms/stop words, optional semantic search | — | open |