feat(#2008): generic command-exit-zero gate-predicate evaluator (#2011)

* feat(#2008): add generic command-exit-zero gate-predicate evaluator

Third-party capability gates declared via check.predicate were rendered for
display but never evaluated (only built-in check.query gates fired; the
security capability's gate worked solely via a hard-coded ship.md branch).

Add a generic, deps-injected gate-predicate evaluator (src/gate-predicate-evaluator.cts)
that dispatches by predicate.kind. Built-in kind: command-exit-zero — runs a
bounded sh -c command at the project root (via shell-command-projection.execTool),
inherits env, exit 0 => pass, non-zero => block, timeout => block, fail-closed.

Wire a 'check predicate' subcommand into check-command-router.cts and extend
the three generic workflow gate-dispatch sites (execute:wave:post, execute:post,
plan:post) to route check.predicate gates to the new evaluator. The two-step
gate contract (command-failure => onError; block => halt) is unchanged.

- src/gate-predicate-evaluator.cts: pure leaf, KIND_TABLE extensible
- src/check-command-router.cts: cmdCheckPredicate + buildPredicateDeps + parsePredicateFlags
- docs/adr/2008-*, docs/reference/gate-predicates.md, docs/how-to/command-exit-zero-gate.md
- tests: 38 unit + integration tests (exit mapping, timeout, interpolation,
  property-based bijection, malformed-predicate fail-closed, real subprocess e2e)

Closes #2008

* docs(#2008): backfill changeset pr number 2011

docs/adr/README.md

@@ -63,6 +63,7 @@ See **[CONTRIBUTING.md — "Proposing an ADR or PRD"](../../CONTRIBUTING.md#prop
 | [1593-skill-mapping-converter-methodology.md](1593-skill-mapping-converter-methodology.md) | Skill mapping & converter methodology across runtimes | Accepted |
 | [1769-state-md-transition-module.md](1769-state-md-transition-module.md) | STATE.md Transition Module — intent-based transitions over scattered RMW callbacks | Proposed |
 | [1817-state-md-rebuild-derivability-contract.md](1817-state-md-rebuild-derivability-contract.md) | STATE.md rebuild — derivability contract (capstone 11th transition) | Accepted |
+| [2008-command-exit-zero-gate.md](2008-command-exit-zero-gate.md) | Generic gate-predicate evaluator with a `command-exit-zero` kind (#2008) | Accepted |
 
 ## Seam map