release: prepare Phase 1 Experimental 0.4.3

[codeacme17]

Rationale

Prepare the next coherent Phase 1 Experimental candidate from the changes merged since v0.4.2. This keeps Phase 0 Stable 0.3.2 on npm latest and publishes 0.4.3 only through the protected experimental workflow.

Tracks #210. The release issue remains open until protected publication and public smoke are complete.

Release contents

• styled Human Version and complete Handoff interaction flows
• default-safe in-process Project Toolchain migration
• exact 0.4.2-to-0.4.3 migration guidance while preserving the historical 0.4.1-to-0.4.2 path
• coherent 0.4.3 package, Plugin, Skill, documentation, governance, and candidate digest updates
• complete release-range issue, PR, and contributor inventory

Validation

• npm ci --ignore-scripts
• npm run build and npm run check:skills
• npm test
• npm run validate:acceptance
• npm run validate:p0
• npm run validate:p1 -- --require-publish-ready
• npm run validate:release -- --tag v0.4.3
• npm run test:artifacts
• npm run test:p1-exact-artifacts
• node scripts/verify-experimental-release.mjs --phase candidate --json
• Standards review — passed after release inventory/link fixes
• Spec review — passed after preserving both exact migration paths

All five 0.4.3 npm versions are currently unused. Registry dist-tags remain latest=0.3.2 and experimental=0.4.2 before publication. Local npm trust list verification requires an authenticated npm owner session and returned 401; the protected tag must not be created until the five Trusted Publisher records are verified.