fix: prevent Codex plugin cache drift

[kforris]

Summary

• derive the Codex plugin cache version from a deterministic digest of the complete plugin payload
• make npm run check fail when plugin content changes without a matching cache key
• refresh the bundled plugin so the context-quality tool and explicit projectHint writeback schema from fix: harden context integrity and health #11 reach installed Codex clients
• document the expected <marketplace>/<plugin>/<version> cache hierarchy and distinguish shortened-path errors from real source/cache drift

Verification

• npm run check — 58 passed, 8 gated skips
• npm run format:check
• npm audit --omit=dev --audit-level=high — 0 vulnerabilities
• swift test --package-path apps/BoronMenuBar — 5 passed
• swift build -c release --package-path apps/BoronMenuBar
• codex plugin add boron-context@boron-context --json
• installed payload matches the source bundle with diff -qr
• installed MCP reports get_context_quality_health and requires projectHint for record_activity