Fix: git in Docker builder (page dates) + serve raw .md as text/markdown

[buddies2705]

Two production issues found by testing the deployed site after #223/#224.

1. Docker builder has no git → all page dates are missing

node:20-alpine ships without git, and Docusaurus derives several things by shelling out to git log:

Feature	Live site	Same commit built locally (git present)
sitemap <lastmod>	❌ 0 of 573 URLs	✅ 532 entries
"Last updated on … by …" footer (showLastUpdateTime/Author)	❌ missing on all pages	✅ present
TechArticle datePublished/dateModified (JSON-LD)	❌ missing	✅ present

The "Last updated" footer has been silently missing in production on every page — pre-existing, not caused by recent work. Adding lastmod in #224 is what made it visible.

Fix: RUN apk add --no-cache git in the builder stage.

Requires the build context to include .git (there is no .dockerignore, so it does today) and a non-shallow checkout. If .git were absent the failure mode is simply that dates stay missing — the build does not break.

2. Raw .md twins served as application/octet-stream

The raw markdown twins at /docs/**/index.md (emitted by plugins/llms-txt.js for LLM/agent consumption) had no mime type, so browsers download them instead of displaying and some crawlers skip them — defeating the purpose.

curl -sI https://docs.bitquery.io/docs/graphql/data-coverage-retention/index.md
-> content-type: application/octet-stream

Fix: nginx regex location setting default_type text/markdown + charset utf-8.

Testing note

I could not build the Docker image locally (no Docker in my environment) and nginx isn't installed to run nginx -t — the config was checked structurally (balanced braces, all directives terminated). Please confirm the image builds and nginx starts cleanly on deploy.

Verification after deploy

curl -s https://docs.bitquery.io/sitemap.xml | grep -c "<lastmod>"          # expect ~530, currently 0
curl -sI https://docs.bitquery.io/docs/graphql/data-coverage-retention/index.md | grep -i content-type   # expect text/markdown

🤖 Generated with Claude Code