release: prepare 0.12.0 release notes and version bump

[Aaronontheweb]

Summary

Cut v0.12.0 covering cache-stable session routing, Slack PDF/document ingress, durable working context, structured compaction, and control-plane write hardening.

Features

• Cache-stable message assembly with volatile User-role tail (feat(sessions): cache-stable message assembly with volatile User-role tail #618)
• Session-sticky LLM routing via X-Session-Id header (feat(providers): session-sticky LLM routing via X-Session-Id header #610)
• llama.cpp timings parsing for cache + performance metrics (feat(providers): parse llama.cpp timings for cache + performance metrics #615)
• netclaw chat -p --resume and --json flags for scripted multi-turn sessions (feat(cli): add --resume and -p flags to netclaw chat for scripted multi-turn sessions #613)
• Audience-gated attachment ingress contract + Slack PDF support (feat(channels): audience-gated attachment ingress contract + Slack PDF support #601)
• Durable WorkingContext grounding that survives compaction and restart (feat(sessions): durable WorkingContext grounding #598)
• Structured compaction summary with monotonic boundary (feat(sessions): structured compaction summary with monotonic boundary #597)
• Containerized netclawd + ephemeral Docker evals (feat(daemon): containerize netclawd and run evals in ephemeral Docker #603)
• Multi-turn conversation eval category (feat(evals): multi-turn conversation category + Personal posture for eval container #616)

Bug Fixes

• Control-plane write gating and lifecycle file hard-deny (fix(security): gate control-plane writes, hard-deny lifecycle files #617)
• Slack attachment contract parity + hardening (fix(slack): attachment contract parity + hardening (#604 follow-ups) #607)
• Claude Code marketplaces and ~/.claude/commands skill resolution (fix(skills): resolve claude-code marketplaces and commands compatibility #599)
• Skills feed deploy pinned to production branch (fix(ci): pin skills feed deploy to production branch #606)

Internal

• Disabled Docker publish job in release pipeline (chore(ci): disable Docker publish job in release pipeline #620)

Test plan

• CI green
• RELEASE_NOTES.md reflects all merged PRs since 0.11.0
• Directory.Build.props version bumped to 0.12.0