Give the registration policy editor real bucket ids

[nbudin]

Fixes #11895

Summary

• RegistrationPolicyBucket#as_json now includes "id", so the registration policy editor can round-trip a bucket's real id through form_response_attrs_json. EditingRegistrationBucket/BucketForRegistrationPolicyUtils carry an optional id (absent for a bucket added in the current edit session) so RegistrationPolicy#sync_buckets_from_hash! can correlate edited buckets by id instead of falling back to key.
• Converted the handful of RegistrationPolicyBucket#key business-logic usages that were directly convertible to id with no backend/schema changes:
  • React list keys in EventCapacityDisplay.tsx/RunCapacityGraph.tsx
  • SignupOption's identity in buildSignupOptions.ts
  • a bucket-to-bucket comparison in SignupAdmin/$id/route.tsx
  • the CreateMySignup/CreateSignupRequest/CreateSignupRankedChoice/CreateUserSignup mutations, switching from the deprecated requested_bucket_key argument to requested_bucket_id
  • a few dead bucket.name ?? bucket.key display fallbacks (name is NOT NULL, so the fallback branch was unreachable)
• Ran bin/rails graphql:update to regenerate the frontend generated files after the .graphql query/mutation edits (no backend schema changes — verified schema.graphql/schema.json are unchanged).

Scope note

Filed #11899 separately for a much larger, related sweep: nearly every Signup/SignupRequest/SignupRankedChoice/SignupChange/GroupedSignupCount consumer across signup-admin, signup-moderation, and the event page still reads the deprecated bucket_key/requested_bucket_key scalar fields instead of the already-available bucket/requestedBucket relations. That's a ~20-file migration in its own right and deserves its own review rather than being folded into this PR.

Test plan

• bin/rails test test/models/registration_policy_bucket_test.rb test/models/registration_policy_test.rb
• yarn run tsc --noEmit
• yarn vitest run test/javascript (187 passed, 1 skipped)
• yarn eslint on all changed files (0 errors)

🤖 Generated with Claude Code

[nbudin]

Pushed a follow-up commit in response to a review question about bucket.name ?? '' in RunSignupsTable.tsx: registration_policy_buckets.name is text NOT NULL at the DB level with no custom resolver/validation that could produce nil, so the GraphQL field's null: true was stricter than reality. Tightened it to null: false (a non-breaking direction for an output field) and removed the now-unnecessary fallback.

Comment written by Claude

[nbudin]

Fixed the Minitest CI failure. Root cause: since RegistrationPolicyBucket#as_json now includes id, RegistrationPolicy.build_from_hash(source_policy.as_json) -- used by create_event_proposal.rb and accept_event_proposal_service.rb to clone a policy into an unrelated new record -- started carrying the source's real bucket ids into the clone, since build_from_hash intentionally preserves id for the (unrelated) edit-in-place sync flow. Persisting the clone then collided with the still-existing source rows on registration_policy_buckets's primary key (PG::UniqueViolation).

Fix: added RegistrationPolicy.build_from_hash_as_clone, which strips bucket ids before delegating to build_from_hash, and switched both cloning call sites to it. build_from_hash itself is untouched -- a keyword argument would've been simpler, but breaks its many bare-hash-literal callers (method("a" => 1, "b" => 2) can't be parsed as one positional Hash once the method also declares a keyword parameter).

Also fixed two now-fragile FormResponseChange "records the new policy as new_value" tests that compared the real persisted state (now with real ids) against a let-block policy that's never itself persisted (so it never had ids) -- switched those to equivalent_to? (content, not identity). Added a regression test for the accept-proposal cloning path mirroring the existing create-proposal one, and confirmed it reproduces the exact CI failure when the fix is reverted.

Full suite (1169 tests) and CI's Minitest job should now be green.

Comment written by Claude

[github-actions]

Code Coverage Report: Only Changed Files listed

Package	Base Coverage	New Coverage	Difference
app/graphql/mutations/create_my_signup.rb	🟢 96%	🟢 84%	🔴 -12%
app/javascript/setupI18Next.ts	🟠 72.41%	🟠 65.52%	🔴 -6.89%
app/models/registration_policy.rb	🟢 98.65%	🟢 98.73%	🟢 0.08%
app/services/accept_event_proposal_service.rb	🟢 97.87%	🟢 100%	🟢 2.13%
Overall Coverage	🟢 56.04%	🟢 56.04%	⚪ 0%

Minimum allowed coverage is 0%, this run produced 56.04%