[P2] Designer authoring gaps (live prop, no Studio editor)

[os-zhuang]

Part of the metadata liveness audit umbrella #1878 (P2 — spec hygiene, cluster #7).

Problem

Designer authoring gaps: the property is live (consumed by the runtime) but has no Studio editor, so it can only be authored by hand-editing metadata. Add editors to the relevant Studio panels.

Checklist

• dataset: filter / format / derived / dateGranularity
• skill: triggerConditions (the activation-critical field — currently no editor)
• flow: notify (absent from the static palette)

Evidence

• docs/audits/README.md cluster Remove explicit pnpm version from workflows to fix version conflict #7
• docs/audits/2026-06-datasetschema-property-liveness.md, 2026-06-skillschema-property-liveness.md, 2026-06-flowschema-property-liveness.md