feat: embed publish constraints (required piece + trigger lock)

Supporting ticket for a customer-submitted PR. activepieces/activepieces#13590 is the feature request; this tracks the contributed implementation of it, opened by the customer who asked for it Needs a core-team review and merge, nothing else.

PR

activepieces/activepieces#14076, Jason Fill (jasonfill). Open since Jul 6, last push Jul 20, 4 commits, 951 additions / 11 deletions across 15 files. Auto-closed once by the unsolicited-PR policy on Jul 16, then reopened with keep-open (existing customer, discussed beforehand).

Scope

Two per-flow embed publish constraints on flow.metadata.embedConstraints, no DB migration. Set by the vendor at flow creation via CreateFlowRequest.metadata; the embedded end user cannot change them.

1. requiredPieceNames: string[]. Publish blocked unless a non-skipped step (action or trigger) uses one of the listed pieces. Subflow triggers exempt.
2. triggerLock: 'none' | 'locked' | 'frozen'. locked blocks swapping or clearing the trigger piece with inputs still editable, frozen makes the whole trigger read-only.

Shared helper embedConstraintsUtil in core-execution, re-exported through @activepieces/shared, so UI and server read one source of truth. Server guards in flow.service.ts: publish check in updatedPublishedVersionId(), plus assertTriggerLockAllowsUpdate on UPDATE_TRIGGER and IMPORT_FLOW, both returning 409. UPDATE_METADATA now carries the existing embedConstraints key over. UI greys out Publish with a reason tooltip and hides the trigger Replace affordance. Docs page added at docs/embedding/publish-constraints.mdx.

State

Greptile 5/5 on the latest commit ("safe to merge", no files flagged). Two earlier findings (EMPTY-trigger alignment, service-principal exclusions) already addressed. CLA signed, GitGuardian and mergefreeze green. The CE and EE e2e jobs report skipping, so no e2e ran against this branch.

Tests included: unit coverage for flowSatisfiesRequiredPiece and a 449-line API integration suite (required-piece missing / present / subflow-exempt, locked piece swap, frozen edit, locked input-only edit, and both bypasses).

Blockers

1. Merge conflicts against main. mergeable: CONFLICTING, branch untouched since Jul 20. Rebase needed before anything else.
2. Worth confirming in review: the whole guarantee rests on the UPDATE_METADATA carry-over, since flow.metadata is otherwise builder-writable. Also check scope against activepieces/activepieces#13590, which listed trigger pinning as out of scope for v1.