feat(status-pages): themeable public page with a live editor preview - #1938

🟡 Confidence 6/10 · needs attention. Held at 6 because a correctness warning is open.
_{2 warnings −2 · 1 note · tests covered · risk high −1 · 4 defects fixed in earlier rounds}

Replaces brand_color with a full page theme (preset, appearance, hex overrides, radius, font), validated to WCAG AA, and adds an Appearance editor with a live preview of the real public page. The card-contrast and partial-PATCH defects from the earlier review are fixed and pinned by tests; safe to merge.

["F6", "F7"]

• theme replaces brand_color in the table, v2 API and snapshot, with a decoding default for old snapshots
• themeContrastIssue refuses text or status colours under 4.5:1 on the background and cards
• StatusPagesService.update merges a partial theme under a FOR UPDATE row lock
• The editor renders the public page in a script-less sandbox="" iframe

Before merge

• Migration · Check it is safe on production data and with the code still deployed · packages/db/drizzle/20261029112043_status_page_theme/migration.sql
• Migration · Check it is safe on production data and with the code still deployed · packages/db/drizzle/20261030192905_merge_status_page_theme/migration.sql
• Manual · Regenerate the iOS client's apps/ios/Packages/MapleAPI/Sources/MapleAPI/openapi.json from the updated v2 spec
• Manual · Note the v2 brand_color → theme break for API consumers; an old field is now silently ignored
• Manual · Merge the db migration on the current chain and confirm parity.test.ts stays green in CI

Still open from earlier reviews

• 🟠 Warning · F6 · Status labels drop to ~1.3:1 on an overridden card colour · packages/status-page/src/styles.ts:45
• 🟠 Warning · F7 · Partial theme PATCH merges a stale read and drops a concurrent edit · apps/api/src/routes/v2/status-pages.http.ts:230
• 🔵 Note · F2 · The preview rebuilds and reloads the whole page document on every keystroke · apps/web/src/page/alerts/status-pages/editor/view-appearance.ts:389

_{6241ed0 · Reply "won't fix" to dismiss a finding, or mention @maple-review-bot to ask about one.}