docs: add launch publishing assets

[AlainDor]

Summary

• add the public launch article and link it from README/docs
• move historical planning notes out of docs/ into .planning/
• finalize posting, Codex plugin, and crates.io alpha guidance
• scrub stale research/planning paths from public surfaces and benchmark artifacts

Verification

• cargo build --workspace
• cargo test --workspace
• cargo test --workspace --all-features
• cargo fmt --all -- --check
• cargo clippy --all-targets --all-features -- -D warnings
• cargo deny check
• cargo doc --workspace --no-deps
• cargo publish --dry-run -p mimir-core --allow-dirty
• cargo test -p mimir-harness --test recovery_benchmark
• python3 benchmarks/recovery/test_bench.py
• stale path sweep for docs/planning, research, docs/research, analysis/reports
• mimir status --project-root .