chore: Item 10 — migrate STATE.scm → STATE.a2ml v2 thin journal (#43)

## Estate Tech-Debt — Item 10 (.scm → .a2ml v2 migration)

Migrates `.machine_readable/STATE.scm` (v1 s-expr machine state) to the
canonical **v2 thin session journal** a2ml format.

### Spec
`standards/a2ml-templates/STATE.a2ml.v2.spec.adoc` — v2 stores only
`phase`, `next_action`, `last_action`, `updated`, and `@blockers`.
Everything derivable (session history, milestones, %s, file lists) is
intentionally discarded per the spec ("v2 discards everything
derivable").

### Mapping applied
- `phase` ← `(current-position (phase …))`
- `next_action` ← first `critical-next-actions` item
- `last_action` ← last `session-history` accomplishment
- `blockers` ← `blockers-and-issues` (critical/high/medium/low)
- `updated` ← `(metadata (updated …))`

### Scope / safety
- Source `STATE.scm` removed (v2 is a clean break per spec — "a repo is
  either v1 or v2; no forward-compat shim").
- No build/CI/Justfile recipe references `STATE.scm` in this repo
(verified).
- Residual `.claude/CLAUDE.md` mention is non-executing boilerplate →
follow-up.

Converted by `state_scm_to_v2.py`; output verified against the v2 spec
grammar.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: hyperpolymath <hyperpolymath@users.noreply.github.com>
Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

Author: hyperpolymath

.machine_readable/STATE.a2ml

@@ -0,0 +1,37 @@
+# SPDX-License-Identifier: PMPL-1.0-or-later
+# Migrated from STATE.scm by state_scm_to_v2.py on 2026-05-17
+
+@state(version="2.0"):
+phase: "v0.1-complete"
+next_action: "Complete shell_validator.adb implementation"
+last_action: "Populated comprehensive STATE.scm with project status"
+updated: 2026-01-04
+
+@blockers:
+- id: shell-validator-implementation-needs-com
+  description: "Shell validator implementation needs completion"
+  waiting_on: "high-priority — internal"
+  since: 2026-01-04
+- id: justfile-recipes-are-stubs-need-actual-b
+  description: "Justfile recipes are stubs - need actual build/test/clean commands"
+  waiting_on: "medium-priority — internal"
+  since: 2026-01-04
+- id: no-unit-test-suite-yet-aunit-integration
+  description: "No unit test suite yet - AUnit integration pending"
+  waiting_on: "medium-priority — internal"
+  since: 2026-01-04
+- id: man-page-and-shell-completion-scripts-no
+  description: "Man page and shell completion scripts not created"
+  waiting_on: "medium-priority — internal"
+  since: 2026-01-04
+- id: powershell-config-path-handling-needs-pl
+  description: "PowerShell config path handling needs platform detection"
+  waiting_on: "low-priority — internal"
+  since: 2026-01-04
+- id: cross-compilation-for-macos-and-windows-
+  description: "Cross-compilation for macOS and Windows not configured"
+  waiting_on: "low-priority — internal"
+  since: 2026-01-04
+@end
+
+@end