R1-001: Ratify Deterministic Snapshot Kernel ADR and architecture decision log

[1sgtpepper]

Summary

Ratifies the Deterministic Snapshot Kernel ADR and links it from the architecture overview. The ADR records current versus planned ownership, CompatibilityShell limits, and the executable gates that future R1 work depends on.

Linked issue

Fixes #133.

PR Checklist

• Linked issue checked.
• One layer or one mechanical change.
• Behavior/schema/golden impact checked.
• Tests/docs updated.
• Local checks run.
• Keep draft until required CI is green.

Release target

v1.2.0 / R1 foundations

Single layer changed

Choose one unless this is a mechanical change proven by tests:

• scanner
• parser
• checker
• reporter/schema
• config
• docs/governance
• packaging/CI

Behavior impact

• No user-visible behavior change
• User-visible behavior change
• Diagnostic behavior change
• JSON/SARIF/schema change
• Golden output change

Tests and docs

• Tests added/updated
• Golden files added/updated
• Docs updated
• Limitations updated
• Changelog updated

Dependency checklist

• I checked docs/contributing/pr-dependency-checks.md and updated every dependent artifact.

Local checks

Paste relevant commands and results:

python -m ruff check docs/architecture/deterministic-snapshot-kernel-adr.md docs/architecture.md
# warning: No Python files found under the given path(s)
# All checks passed!

[1sgtpepper]

Replaced by #216 using clean R1 branch naming.