release: Plugwerk 1.0.0 website + docs updates

[bigpuritz]

Track the website / docs work for Plugwerk v1.0.0 (published 2026-05-13) — first stable release.

Following RELEASE_CHECKLIST.md:

• Step 1 — OpenAPI sync (PR chore: sync openapi.yaml from plugwerk 1.0.0 #102) merged into main.
• Step 2 — Compose mirror diff against upstream dist/docker-compose.yml@v1.0.0 is empty; nothing to update.
• Step 3 — Bump hardcoded pre-release example tag in server/deployment.mdx (1.0.0-beta.2 → 1.0.0-beta.3).
• Step 4 — Activate the release banner on the landing page with version: "1.0.0" (no label — the prop was removed).
• Step 5 — Write src/content/docs/releases/1.0.0.mdx (with slug: releases/1.0.0 to bypass Starlight's dot-stripping). Update releases/index.mdx to list it.
• Step 6 — API reference auto-renders, no action.
• Step 7 — Milestone 1.0.0 created (this issue), will close on PR merge. Beta.3 milestone closes once PR docs(server): document the OIDC SSRF guard env vars (#88) #93 merges.
• Step 8 — Open PR, run format + build, merge, smoke-test.

Notable for the release notes

Highlights (knapp, 1-2 Sätze pro Feature):

• S3-compatible object storage backend (#191)
• Admin scheduler dashboard (#516, #517) — enable/disable, dry-run, run-now
• Scheduled orphan-artifact reaper (#496) + storage/DB consistency check (#190) with ShedLock
• Operator-uploadable logos (#254) — top bar, login, favicon
• Effective-config admin view (#522)
• general.site_name in UI (#234)
• Security: undecryptable client-secret detection at startup (#501)

Breaking change:

• Client SDK: PlugwerkUpdateChecker now takes typed InstalledPluginRef (#506). Existing snippets in client-sdk/configuration.mdx and client-sdk/migration.mdx show the old Map.of(...) form — they will mislead readers after 1.0.0 ships. SDK reference doc update tracked separately as a follow-up issue (analog zu docs: update SDK reference for PlugwerkInstaller PluginManager-lifecycle SPI (plugwerk#424) #83 für #424).

Follow-ups (NOT in this PR)

• Dedicated docs for the new S3 storage backend (Configuration page extension)
• SDK reference update for the InstalledPluginRef API change (mirror of docs: update SDK reference for PlugwerkInstaller PluginManager-lifecycle SPI (plugwerk#424) #83 pattern)
• Operator-uploadable-logos admin-page docs (if a server-admin docs section grows)