feat(loops): add a default trigger to new loops

[MattPua]

Problem

New loop forms start without a trigger, requiring an extra click before configuring when the loop runs.

Changes

• Start new loop drafts with an enabled weekly schedule trigger
• Reuse the same trigger factory for additional schedule triggers
• Preserve manual-only loops when the default is removed

How did you test this?

• pnpm --filter @posthog/ui exec vitest run src/features/loops/loopFormTypes.test.ts
• pnpm exec biome check packages/ui/src/features/loops/loopFormTypes.ts packages/ui/src/features/loops/loopFormTypes.test.ts packages/ui/src/features/loops/components/LoopTriggerEditor.tsx
• pnpm --filter @posthog/ui typecheck

Automatic notifications

• Publish to changelog?
• Alert Sales and Marketing teams?

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Created with PostHog Code

[trunk-io]

😎 Merged successfully - details.

[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit f66822c.}

[greptile-apps]

_{Reviews (1): Last reviewed commit: "fix(loops): default new triggers to week..." | Re-trigger Greptile}

[github-actions]

Small, contained UI/business-logic change to loop trigger defaults, outside risky territory, with test coverage and a positive Greptile bot reaction.

• 👍 on the PR from greptile-apps[bot].

Gate mechanics and policy version

Gate		Result
prerequisites	✓	all clear
deny-list	✓	no deny categories matched
size	✓	25L, 2F substantive, 40L/3F incl. docs/generated/snapshots — within ceiling
tier	✓	T1-agent / T1b-small (40L, 3F, single-area, feat)
stamphog 2.0.0b3		.stamphog/policy.yml @ 0305ec2 · reviewed head f66822c