docs(spec): author Jido release subject map

[mikehostetler]

Summary

• add the Spec Led workspace scaffolding and release-time Jido subject map under .spec/
• split the package into 17 current-truth subjects with one ADR for the durable subject-map decision
• wire stable covers: markers into the key guides so the authored specs link cleanly to docs

What’s Included

• .spec/README.md, .spec/AGENTS.md, .spec/decisions/README.md
• .spec/decisions/jido.spec_subject_map.md
• authored subject specs for agents/actions, signals/directives, strategies, runtime lifecycle, plugins/sensors, runtime persistence, thread/memory/identity, pods, multi-tenancy, observability/tracing, debugging/errors, configuration/discovery, worker pools/tooling, integrations/migration, testing/examples, plus package/spec workspace subjects
• spec_led_ex added as a dev/test dependency

Coverage Shape

• subjects: 17
• decisions: 1
• requirements: 51
• source covered: 121/121
• guides covered: 34/34
• tests covered: 159/159

Validation

• mix spec.status --no-run-commands
• mix spec.check --base HEAD~1