feat(platform): give toasts a concise title and description (#1944)

[larryro]

What

Resolves #1944. Splits the shared toast namespace copy into concise title + description pairs and updates every call site to pass both, establishing the title+description convention for toasts.

Changes

• messages/{en,de,fr}.json — restructured the entire toast.success.* / toast.error.* namespace from single-line strings into { title, description } objects. de-CH inherits from de (no override needed). Titles are short headlines; descriptions carry the precise follow-up.
• Call sites — updated all consumers of the toast namespace to pass both title and description:
  • automation-row-actions.tsx, account-form.tsx, branding-form.tsx, organization-settings.tsx, member-add-dialog.tsx, configuration.tsx, forced-change-password.$id.tsx
  • use-convex-mutation.ts — generic error fallback now uses error.generic.title + error.generic.description
  • entity-delete-dialog.tsx / use-delete-dialog.ts — added an optional successDescription so the shared delete dialog renders success.deleted as title + description
• .claude/skills/react/SKILL.md — documented the title+description convention so new toasts follow it.

Verification

• bun run --filter @tale/platform test (i18n suite) — green: parity + usage (orphan-key) checks pass for the new nested keys across all locales.
• bunx tsc --noEmit (platform typecheck) — green.
• bunx oxlint on changed files — 0 warnings, 0 errors.
• bunx oxfmt --check on changed files — clean.

Notes

• Scope follows the issue's concrete "Proposed change": the shared toast namespace + its call sites. Feature-local toasts that already pass a title (and often a description) are unaffected; the new convention bullet guides future ones.
• No docs/ change: this refines existing micro-copy within shipped features rather than adding a documented feature surface.