chore(openspec): drop 9 superseded proposals + 11 stub archive files

Drop 9 batch proposals that are superseded by the boocode-lift-analysis
(boocontext-audit, conductor upgrades, self-healing/verify-gate skills):
add-3tier-memory, import-llm-evaluator, import-pregel-engine, plugin-platform,
conductor-evolution, code-intelligence-upgrade, dev-workflow, ui-overhaul,
agent-reliability.

Delete 11 stub archive files (49-66B each, 'Status: Shipped. Archived.' only)
that provide zero documentation value over the existing CHANGELOG.md + git tags.

openspec/changes/archived/2026-06-07-boocontext/specs/codebase-health/spec.md

@@ -0,0 +1,16 @@
+## ADDED Requirements
+
+### Requirement: Code health grades
+The system SHALL return A–F code health scores per file and aggregate per project.
+
+#### Scenario: File health score
+- **WHEN** a file is analyzed for code health
+- **THEN** it SHALL receive a score from 10.0 (optimal) to 1.0 (worst)
+- **THEN** the score SHALL be mapped to A–F grade
+
+### Requirement: Hotspot detection
+The system SHALL identify technical debt hotspots — files with high revision count and low code health.
+
+#### Scenario: Hotspots listed
+- **WHEN** a project is scanned for hotspots
+- **THEN** files with high churn and low health SHALL be ranked