…r nav

Switch the "Changelog" anchor in the sidebar (and footer) from
https://trunk.io/changelog to a local /changelog landing page that
surfaces the auto-generated changelog drafts produced by the Mintlify
changelog feature (added in #25).

- `changelog/index.mdx` — landing page listing the 3 May 18 entries as
  Mintlify `<Update>` blocks, each linking to its full draft.
- `docs.json` — anchor + footer href swapped from external trunk.io URL
  to `/changelog`. New hidden `Changelog` tab claims ownership of
  `/changelog/*` routes so the top-bar tab indicator stays correct
  (without the tab, Mintlify falls back to the last visible tab —
  Code Quality — when on changelog pages).
- `.mintignore` — `changelog/` is commented out so the auto-generated
  drafts build and route locally.

Staged for team buy-in on moving the changelog from the marketing site
to the docs site. Stacked on #25 — needs that PR's 3 changelog drafts
to render correctly.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Expand the changelog work from a minimal nav swap to a full migration
of every historical changelog entry from the marketing site to the
docs site, using Mintlify's native <Update> component.

Content:
- 150 historical entries imported from the closed marketing-site
  PR #609 (trunk-io/marketing-site) into `changelog/*.mdx`. Combined
  with the 3 May 2026 bot drafts already on this branch, the docs
  site now hosts 153 entries spanning 2023-08-01 → 2026-05-18.
- 68 image assets copied into `assets/changelog/` (221 MB). Image
  paths in MDX rewritten from `/changelog-assets/<file>` (marketing
  convention) → `/assets/changelog/<file>` (Mintlify convention).
- Every entry has a `description:` frontmatter field — auto-extracted
  from the first prose paragraph (announcement-style entries) or the
  first 1-2 bullets (release-note-style entries like Plugins X.Y.Z),
  stripped of markdown and YAML-escaped. The 3 bot drafts keep their
  hand-written descriptions.

Nav and rendering:
- `changelog/index.mdx` is the canonical unified changelog at
  `/changelog`. Year + month nested headings (`## 2026` → `### May 2026`)
  with unique anchor IDs, Mintlify's built-in `<Update>` tag filter
  pills for per-category filtering, and `rss: true` for an automatic
  feed.
- `merge-queue/changelog.mdx` and `flaky-tests/changelog.mdx` are
  per-product changelog pages (only the entries tagged for that
  product), embedded in their respective product tabs. Same
  generator, scoped to one category. RSS feed per product.
- `docs.json` — hidden `Changelog` tab now claims `/changelog/*`
  routes with a year-grouped sidebar (2026/2025/2024/2023). The
  `Merge Queue` and `Flaky Tests` tabs each get a "Changelog" page
  at the end of their main group.
- `.mintignore` — `changelog/` line commented out so the directory
  builds.

Category rename:
- The "Merge" category is renamed to "Merge Queue" across all 34
  affected entries so the tag-filter UI shows the full product name.

Cross-repo dependency:
- trunk-io/marketing-site#613 (draft) sets up 150 per-slug 301
  redirects from trunk.io/changelog/<slug> to the new
  docs.trunk.io/changelog/<date>-<slug> locations, plus `/changelog`
  → `docs.trunk.io/changelog`. That PR is held until this one ships.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>