feat(docs): generate plugin docs + badges from the e2e run

[omar-nahhas]

Two new devkit targets, so this is built once in the devkit rather than hand-made four times.

make docs — DEC-077

Every green e2e already captures one screenshot per BDD scenario, and each scenario title is a plain-English statement of a behaviour the plugin guarantees. Both were being thrown away: screenshots expired as CI artifacts, feature files were read only by developers.

Fleet state today: chat-comments has zero images in its README; the other three have hand-captured ones that go stale with no signal.

make docs joins them into docs/BEHAVIOUR.md + docs/screenshots/. Because the source is a passing run, a screenshot cannot depict a state the plugin no longer produces, and a renamed or deleted scenario drops out of the docs automatically. Captions are scenario titles verbatim — the generator invents no prose, and a scenario with no captured screenshot says so rather than being silently omitted.

The subtle part. Playwright truncates long scenario titles in its result directory names and inserts a hash:

chat_comments-tests-e2e-features-10-comm-6bdad-an-be-commented-BEH-5-BEH-8--test-finished-1.png

so matching back to the feature file cannot be an exact comparison. It matches on the longest shared run of trailing tokens (the tail survives truncation), requiring at least two — one shared token is meaningless in a file where every scenario says "comment". My first version missed this and produced a document where all twelve scenarios reported "no screenshot" — a plausible-looking empty result rather than an obvious failure. test_docs_from_e2e.py pins this with real artifact names.

Verified against the real chat-comments artifact and feature file: 11/12 scenarios illustrated (the 12th is the devkit's own lifecycle scenario, correctly absent from the plugin's feature file).

make badges — DEC-078

The e2e suite is the strongest quality claim these plugins have — nested real A0, real browser, and a seam-off red-proof that fails the build if the scenarios could pass with the plugin not installed. None of it was visible to a reader:

repo	badges today
chat-comments	0 (the one match was a Mermaid node, not a badge)
diff-visualizer	0
mermaid-diagrams	0
share-chat	1
development-testkit	5

make badges splices a standard block under the H1, idempotently, between BADGES:START/BADGES:END markers (verified: applying twice yields one block).

Constraint on the content: every badge must be independently checkable by clicking it. Workflow status, release tag and licence are all GitHub-generated. The single static label ("BDD e2e") links to the actual feature directory. No invented coverage percentages.

Follow-up, not in this PR

• Applying both targets across the four plugin repos.
• Marketplace cards: none of the four plugins is currently listed in the index at all — omar-nahhas/a0-plugins/plugins/ has no entry for them. The schema supports up to 5 screenshots URLs plus a ≤20 KB square thumbnail, so the generated screenshots feed it directly once the entries exist.