feat(alerts): rule editor as sentence cards with plain summaries - #2425

🟢 Confidence 10/10 · safe to merge. No defect found in the editor state, summaries, card a11y or chart paths I read; the lab fixtures and the new scene-test files were only partly read.
_{no findings · tests covered · risk medium}

The alert rule editor becomes sentence cards with plain one-line summaries, cards that stay open while they hold a save blocker, and one action bar that turns Save into a validation attempt. Presentation and editor state only; safe to merge.

• sentenceCard/sentenceChain kit primitive with disclosure button, header h2 and focus return to the summary
• summary.ts pure summaries per card: watch, condition, notify, name
• Save is pressable with blockers: ClickedSave reveals field errors and focuses the first one
• ruleChart gets a real empty/loading text state and clips its series to the range

Production impact

_{145b4c4 · Reply "won't fix" to dismiss a finding, or mention @maple-review-bot to ask about one.}