feat: render a report as a Markdown page for a GitLab wiki

[lesnik512]

Adds release-scope render report.json -o report.md. It turns a collected report into a Markdown page for a GitLab wiki without calling GitLab.

Page

• Title, collection time in UTC, and a legend: ✅ success · ❌ failed · 🔄 running · ⏭ canceled or skipped · ⚠️ warning or allowed failure.
• A summary table of the services that need attention: failed first, then skipped, then those with changes. It has one column per environment (production first, each ref linked to its deploy job), a Pending cell (N changes · untagged head) and a failures cell (❌ blocking · ⚠️ N allowed).
• Up-to-date services collapse into one <details> table showing their production refs.
• For each service with changes or problems, a section with:
  • its error or warnings
  • the environment line and counts
  • a collapsible table: tag linked to its pipeline (or "⚠️ no pipeline"), one line per MR or the direct commit, Jira keys, where it's deployed, and the failed jobs of the main-branch and tag pipelines. Allowed failures are marked "(allowed)" and a failed trigger job links its child pipeline.
• User text in cells is escaped: |, brackets, </>, and newlines become <br>. Link targets encode space, ) and |.
• GitLab needs blank lines around the Markdown inside <details>; this follows the GitLab Flavored Markdown docs.

Design

• The page code is plain Python in a pure _render.py, with no template engine and no new dependency.
• render exits 2 on an unreadable or unknown-schema report and 1 when it can't write the page. It writes the file atomically.
• collect gets no --markdown flag. The README chains the two commands with ; rather than &&, because collect exits 1 exactly when the page should show a failed service.
• The summary counts blocking and allowed failures separately. The glossary's "Failed job" includes allow_failure jobs, and important jobs that are allowed to fail still matter, just less.
• Page wording says "changes" for rows. Code identifiers follow the glossary's "row".

Checks

75 tests pass at 100% coverage. They include a golden test of a full page with services that are changed, up to date, failed and skipped. I haven't yet checked the result rendered in a real GitLab wiki.