feat: deepen ACTION scope behind action_scope(ctx)

[lesnik512]

What

Two things, on one branch:

1. Feature — a public action_scope(ctx) context manager so commands reach Scope.ACTION dependencies without touching modern_di's container interface:

   @app.command()
   @inject
   def my_command(ctx: typer.Context) -> None:
       for job_name in job_names:
           with action_scope(ctx) as action:
               action.resolve_provider(Dependencies.job).run()

2. Planning convention — adopt the portable two-axis convention from lesnik512/planning-convention (v1.0.0), as applied in the sibling modern-di repo, replacing the single CONTEXT.md.

Feature: deepen ACTION scope

Before, ACTION scope leaked build_child_container() to every call site (the command injected modern_di.Container and built a child by hand). REQUEST scope was deep behind @inject; ACTION was shallow. This pulls scope-nesting behind one named interface — leverage (one interface for every scope) and locality (nesting lives in action_scope).

• Multiple actions per command preserved — each with action_scope(ctx) block is its own ACTION container (the loop case ACTION exists for). See planning/decisions/2026-06-25-action-scope-multiple-actions-per-command.md.
• @inject now always builds the per-command REQUEST container and stashes it on ctx.meta (per-invocation, isolated — not ctx.obj, shared app state), so request-scoped singletons are shared between injected params and action-resolved deps.
• The manual FromDI(Container) pattern still works and stays tested (backward compatible).

Planning convention

• architecture/ — living capability truth (scopes.md, injection.md); the promotion target.
• planning/ — .convention-version, README, index.py validator/indexer, _templates/, changes/, decisions/, deferred.md.
• Seeded with the real artifacts for this change (the 2026-06-25.01-action-scope bundle + decision); deferred.md records the still-open ctx.obj container-seam candidate.
• lint-ci runs planning/index.py --check; adds just index / just check-planning; CLAUDE.md points at architecture/ and planning/.

Verification

just test-ci — 11 passed, 100% coverage (planning/index.py is never imported, so the --cov=. gate is unaffected). just lint-ci clean (ruff + planning validation). just check-planning → planning: OK.

🤖 Generated with Claude Code