🚀 Release 8.2.0 (#1739)

Prepares the **8.2.0** release.

## Version bumps

- `sphinx_needs/__init__.py` → `8.2.0`
- `.github/workflows/docker.yaml` (`NEEDS_VERSION`) → `8.2.0`
- `docs/_static/tutorial_needs.json` regenerated with the new version

## Changelog

Rewrote the `Unreleased` section into a user-friendly `8.2.0` entry.
Reviewing every PR since v8.1.1 surfaced several that were missing from
the draft (notably the full variant-data feature set), so those are now
included and categorised.

The entry leads with the two headline features:

- **Variant data** — a dedicated narrative section tying together the
new variant-data tooling (#1715, #1716, #1721, #1737):
`needs_variant_data` / `needs_variant_data_file`, the inline `<{ ... }>`
field syntax, the `variant` role, and the `if` directive — with runnable
examples showing the shared `var` namespace across filters, fields,
prose, and whole blocks.
- **`network_back` schema validation** (#1731) — incoming-link
validation, letting coverage rules ("every requirement must be covered
by a test") be expressed once on the target.

Remaining changes are grouped into **Improvements** (#1632, #1717,
#1736, #1730, context7), **Deprecations** (`needs_filter_data`),
**Breaking changes** (Open-Needs removal, #1732), and **Bug fixes**
(#1727, #1371, #1564). Internal/test-only PRs were intentionally
omitted.

Docs build cleanly — all cross-references in the new section resolve
without warnings.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---
_Generated by [Claude
Code](https://claude.ai/code/session_01HQwraRU189oRFK5j4yRiYo)_

---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: chrisjsewell

.github/workflows/docker.yaml

@@ -16,7 +16,7 @@ on:
     paths: ['docker/**']
 
 env:
-  NEEDS_VERSION: 8.1.1
+  NEEDS_VERSION: 8.2.0
   DEPLOY_IMAGE: ${{ github.event_name != 'pull_request' }}
 
 jobs: