_data metadata gaps: untagged examples, undefined/unused tags, stale "experimental" labels

Problem

_data/examples.json and _data/tags.json drive the README table and the web app's tag navigation, and they've drifted:

• 4 examples have empty tags (required per _data/README.md), making them invisible to anyone browsing by tag: editable-block-1b8c51, inner-blocks-dcd824, recipe-card-744e8a, settings-sidebar-82c525.
• 2 tags are used in examples.json but undefined in tags.json: block and experimental — their filter links in the web app lead nowhere useful.
• 1 tag is defined but never used: gutenberg-plugin.
• Stale stability labels: experimental is applied to the Interactivity API countdown, and several tags.json descriptions still call the Interactivity API experimental — it has been stable in core since WP 6.5.

Proposed fix

1. Tag the 4 untagged examples (proposals — maintainer-reviewable):
   • inner-blocks-dcd824 → new tag inner-blocks + static-rendering
   • editable-block-1b8c51 → static-rendering (covers its build and no-build editable blocks)
   • recipe-card-744e8a → static-rendering
   • settings-sidebar-82c525 → new tag inspector-controls (nothing in the current vocabulary covers block settings sidebars)
2. Delete the experimental tag from examples.json and remove the generic block tag (too broad to filter on) — or define them if there's a reason to keep them.
3. Remove or use gutenberg-plugin (currently dead weight; likely removable once Gutenberg leaves the wp-env setup, see #151).
4. Reword tags.json descriptions that still call the Interactivity API experimental.
5. Add a _data validation step to CI (in static-linting.yml, via the existing _bin tooling): every used tag is defined, every example has ≥1 tag, no defined tag is orphaned, every examples.json slug has a matching plugins/ dir and vice versa. This is what prevents this issue from recurring.
6. Run npm run table:update to regenerate the README table.

Out of scope

• Plugin code/header changes (#150) and wp-env changes (#151).

Start with _data/README.md, _data/examples.json, and _data/tags.json to verify the metadata requirements and proposed tag changes. Then inspect the existing _bin tooling and static-linting.yml before adding the validation step, and run npm run table:update. Done means the metadata is consistent, the validation covers the listed invariants, and the README table is regenerated.