#2684 gatorwalk-factory: starter plugins (GW-13)

Part of the gatorwalk-factory rebuild of @swamp/software-factory (gatorwalk-factory/ in swamp-extensions). Shipped so far: GW-1..GW-9, the swamp-extensions lifecycle (#2630) and the tracker contract with the Linear adapter (GW-16, #2664). Read gatorwalk-factory/README.md and DESIGN.md first.

Depends on GW-12 (#2663, plugins by eject): do not start until it has merged. GW-12 was narrowed to eject only, so a plugin is a working starting point a lifecycle copies (eject), not a dependency it references.

Ship the starter set as plugins a team ejects into its lifecycle and then edits: plan, review-plan (adversarial, producing findings), implement, review (code review) and verify (run tests or CI and record the outcome, which every multi-stage lifecycle in the evidence has). Each has a contract (inputs, outputs, named exits), parameters with sensible defaults (e.g. blocking severities, reviewer skills), and prompts written for an agent following the gatorwalk skill. Take the stage designs from what already works: lifecycles/build-swamp-extension.yaml and lifecycles/swamp-extensions.yaml.

Tests: each plugin validates and passes GW-9's graph analysis on its own; ejecting the set composes a lifecycle equivalent to build-swamp-extension's core that validates clean; and a work item runs through an ejected lifecycle on the real engine (integration/). The launch templates built from these are GW-15. Nothing is published.