fix(tasks): use autocomplete for creator in loop admin

[charlesvien]

Problem

Opening a Loop's change page in Django admin never finishes loading.
LoopAdmin configures widgets for team, created_by and sandbox_environment, but the creator FK (added alongside the admin in #70604) was never listed in autocomplete_fields, raw_id_fields or readonly_fields.
Django falls back to a plain <select> for it, which queries every row of posthog_user and renders each one as an <option>, so the page hangs on any install with a real user table.

Changes

Adds creator to autocomplete_fields on LoopAdmin, matching how created_by (same target model) is already handled.
Kept it editable rather than readonly so an admin can repair a creator nulled out by SET_NULL after a user deletion.

How did you test this code?

I (or, actually Claude) verified UserAdmin defines the search_fields that autocomplete requires and ran manage.py check --tag admin, which passes with no issues.
No manual load of a production admin page was done.
No test added: a one-line admin widget config isn't a realistic regression target beyond Django's own system checks.

👉 Stay up-to-date with PostHog coding conventions for a smoother review.

Automatic notifications

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

Docs update

N/A, internal admin only.

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

Diagnosed and authored with Claude Code.
Starting from a report that the Loop admin page loads forever, Claude enumerated the FKs on Loop, found creator was the only one without a widget config and confirmed via git history that it shipped in the same PR as LoopAdmin.
Considered making creator readonly since the model treats it as immutable, but chose autocomplete so support can still fix a nulled creator.
No skills were invoked.

[trunk-io]

😎 This pull request was merged.

[greptile-apps]

_{Reviews (1): Last reviewed commit: "add creator autocomplete to loop admin" | Re-trigger Greptile}

[stamphog]

Trivial one-line Django admin autocomplete fix by an owning-team author with strong familiarity; no risky territory, no outstanding concerns.

• Author wrote 100% of the modified lines and has 11 merged PRs in these paths (familiarity STRONG).
• 👍 on the PR from greptile-apps[bot], hex-security-app[bot].

Gate mechanics and policy version

Gate		Result
prerequisites	✓	all clear
deny-list	✓	no deny categories matched
size	✓	2L, 1F substantive — within ceiling
tier	✓	T1-agent / T1a-trivial (2L, 1F, single-area, fix)
stamphog 2.0.0b3		.stamphog/policy.yml @ 54df693 · reviewed head 6c5f33e

[deployment-status-posthog]

Deploy status

Environment	Status	Deployed At	Workflow
dev	✅ Deployed	2026-07-23 06:13 UTC	Run
prod-us	✅ Deployed	2026-07-23 06:28 UTC	Run
prod-eu	✅ Deployed	2026-07-23 06:30 UTC	Run