#2732 gatorwalk-factory: add issue-lifecycle's complete shortcut to swamp-extensions.yaml as per-stage exits (gap 6)

Part of the gatorwalk-factory rebuild (gatorwalk-factory/ in swamp-extensions). This closes gap 6 in lifecycles/swamp-extensions.md, following the decision recorded on #2668: a shortcut from several stages to one is expressed per stage, with no new format construct.

Sequencing: start after #2730 has merged. #2730 also edits swamp-extensions.yaml (it removes the lowered maxCycles), and these exits add paths the graph analysis has to count.

What to do

issue-lifecycle's complete goes straight to notify from implementing, pr_open or releasing, when the normal path does not apply. It requires code-conformance-clear and verification-clear. swamp-extensions.yaml keeps only the releasing case today (release evidence completed).

Add a manual complete exit to notify from each gatorwalk stage that corresponds to the other two cases, gated on what issue-lifecycle checks there:

• "From implementing". issue-lifecycle's implementing phase covers what gatorwalk splits into implement, conformance-review and verify. Its complete requires conformance and verification to be clear, so in gatorwalk the exit belongs where both are satisfied: verify or attest, not implement. Choose one and say why.
• "From pr_open": the pull-request stage, or merge, whichever matches issue-lifecycle's pr_open.
• "From releasing": already present.

Gates:

• Each exit is manual: true, because complete is a person's decision.
• Use cel gates to require conformance clear and verification passed, bound to the change-summary commit as the other exits past implement are. cel reads the latest evidence from whichever stage recorded it; evidence-recorded reads only the current stage.
• Check issue-lifecycle's own complete for anything else it requires.

Done when

• The exits are in swamp-extensions.yaml, and validate passes with no new errors and no new ambiguous-exit warnings.
• The lifecycle walk tests cover each new complete exit, and cover its refusal when conformance or verification is not clear.
• swamp-extensions.md records the new exits in the Phases table and marks gap 6 resolved, keeping its number and citing #2668.

Out of scope

• Any format change. The decision on #2668 is per-stage exits.
• Gap 1 (the lifecycle acting on the Lab) and gap 7 (restart semantics).