docs(capabilities): create 'agents' group + tag audit_dod_schema

New capability group page docs/capabilities/agents.md consolidating:
- agent_launch_worktree_go_infra
- agent_cleanup_worktree_go_infra
- audit_dod_schema_go_infra (added 'agents' tag to its frontmatter)

3 functions = minimum for a capability group page. Adds row to
docs/capabilities/INDEX.md. End-to-end example shows the launch ->
work -> cleanup -> dod-audit cycle that agent_runner_api (0113)
will orchestrate.

functions/infra/audit_dod_schema.md

@@ -7,7 +7,7 @@ version: "1.0.0"
 purity: impure
 signature: "func AuditDodSchema(issuesDir, flowsDir string) (DodSchemaReport, error)"
 description: "Escanea dev/issues/ y dev/flows/ (incluidos subdirectorios completed/) y para cada .md parsea el bloque dod_evidence_schema del frontmatter YAML. Valida que cada item tenga id unico, kind in {screenshot,log,url,cmd}, expected no vacio y required bool (default true). Read-only: no modifica nada. Devuelve un DodSchemaReport con files (uno por archivo con items o errores), totales y conteo de items invalidos. Tolerante a frontmatter ausente o malformed — registra el error en el archivo afectado y continua."
-tags: [doctor, dod, evidence, frontmatter, taxonomy, validator]
+tags: [agents, doctor, dod, evidence, frontmatter, taxonomy, validator]
 uses_functions: []
 uses_types: []
 returns: []