feat(skills): добавлен скилл brainstorm-with-docs (v1)

- Зачем:
  - нужен ручной скилл для брейнсторма и дизайна, который удерживает
    словарь смыслов (CONTEXT.md) и лёгкие ADR, активно прожаривает план
    и не сваливается в реализацию.
- Что:
  - SKILL.md: процесс (контекст → классификация → декомпозиция →
    грилл → синтез опций → подтверждение → артефакт), единый HARD-GATE
    «исследуй, но не меняй состояние» с поправкой на auto mode.
  - artifacts/: шаблоны spec, research-note, adr, runbook, prd, context
    (по файлу на тип для progressive disclosure).
  - README.md с MIT-атрибуцией grill-with-docs (Pocock) и brainstorming
    (obra/superpowers); шов для будущей фазы дивергенции в шаге 5.
  - frontmatter переносим: Claude читает все поля, Codex — name+description.
- Проверка:
  - python3 yaml-парс frontmatter; markdown-ссылки на artifacts/ резолвятся.

agents/.agents/skills/brainstorm-with-docs/artifacts/spec.md

@@ -0,0 +1,56 @@
+# Solution Design / Spec
+
+Use for engineering, architecture, DevOps, integration, migration, or any
+non-product feature work where a direction has been chosen but not yet built.
+
+Use the smallest version that preserves the useful thinking. Drop sections that
+add nothing for this particular problem — an empty section is noise.
+
+## Template
+
+```markdown
+# Title
+
+## Problem
+
+## Context
+
+## Goals
+
+## Non-goals
+
+## Current state
+
+## Options considered
+
+## Recommended approach
+
+## Rationale
+
+## Decisions and rejected alternatives
+
+## Risks and mitigations
+
+## Validation
+
+## Documentation impact
+
+## Open questions
+```
+
+## Notes on key sections
+
+**Decisions and rejected alternatives** is the highest-value section. Capture:
+
+- accepted decisions and the reason behind each
+- rejected alternatives and *why* they were rejected
+- subtle constraints and important defaults
+- sequencing decisions
+- assumptions future agents must not silently re-derive
+
+Do not turn this section into an ADR dump. Promote a decision to its own ADR
+(`artifacts/adr.md`) only when it is durable, surprising, and the result of a
+real trade-off.
+
+**Validation** describes how we will know the implementation is correct — tests,
+checks, acceptance criteria. It belongs here, not in `CONTEXT.md`.