#2611 gatorwalk-factory: lifecycle holder and work-item model type (GW-6)

Part of the gatorwalk-factory rebuild of @swamp/software-factory. GW-1..GW-5 shipped (#2576, #2584, #2588, #2598; PRs 327-329, 333). GW-6 turns the runtime library into model types a person or agent can run with swamp model method run. It is the last step before the driving skill (GW-8), after which gatorwalk can build itself.

Scope, from the rebuild plan:

• A lifecycle holder model type: an instance whose globalArguments hold a team's lifecycle, validated by the GW-2 schema when the definition is saved. Work items read it raw through the definition repository (one file read, which also works on remote workers), not through the catalog.
• A work-item model type: one instance per work item, identified by a swamp-generated key (not a ticket number); tracker ids are kept as data. start copies the holder's lifecycle into a fixed lifecycle resource on the work item, which pins the run to that version (not into globalArguments, which direct execution can overwrite).
• Methods over the GW-4/GW-5 runtime: start, status (current stage, dispatch packet, each exit's readiness including cycle limits, open validations), record_artifact, record_evidence (rejections returned, not thrown), dispatch, record_usage, approve and decline, grant_override, advance, reset. Each writing method takes the caller's expected stage, cycle and era, and records the actor from tagOverrides.initiatedBy. status is a read method, so it takes no lock.
• Resource specs (run, artifact, evidence, lifecycle) with retention that never drops a product version the run or an approval still references.

Obligations carried from GW-4 and GW-5:

• Store product payloads in their JSON-safe form, so the stored version matches its digest.
• Make run records written before GW-5 readable (overrides defaults to empty) or bump the run schema version, before anything is stored.
• Document that the first start of a new work item takes no per-instance lock (swamp gap; plan gap G19).

Out of scope: the driving skill (GW-8), the real-engine test harness (GW-7), trackers (GW-16..18), the summary report (GW-19). Nothing is published: gatorwalk-factory stays manifest-free until go-live.