fix(release): prepare ProjectAtlas v0.4.3

[styler-ai]

Summary

• prepare the v0.4.3 bugfix candidate with the complete token TUI atlas, correct version surfaces, optional-Git behavior, BOM support, purpose-curation guidance, and relation-row validation
• make the release gate exercise the installed candidate across CLI, all advertised MCP tools and their real SQLite effects, v0.3.26/v0.4.0/v0.4.1 compatibility, the persistent bug(mcp): Windows Git config discovery exceeds deadline while CLI succeeds #409 SwipingGale-like stdio scenario, no-Git operation, upgrade, installer, and platform behavior
• harden Codex plugin replacement and recovery on Windows and POSIX with fail-closed locking, path validation, retained crash-recovery snapshots, and hostile rollback coverage
• preserve the requested README About sentence exactly and leave the existing README TUI image unchanged

Refs #411, #427, #428, #432, and #433.

Validation

• cargo fmt --all -- --check
• cargo check --workspace --all-targets --all-features
• cargo clippy --workspace --all-targets --all-features -- -D warnings
• cargo test --workspace --all-features
• cargo test --doc --workspace --all-features
• RUSTDOCFLAGS=-D warnings cargo doc --workspace --no-deps --all-features
• PowerShell and Git Bash installer syntax checks
• openspec validate close-v043-release-regressions --strict
• openspec validate route-purpose-curation-to-low-cost-agents --strict
• python .github/scripts/issue-checklists.py --repo styler-ai/ProjectAtlas
• full repository pre-push gate, including dependency policy, strict string contracts, real scan/lint, release-gate selection, and packaged regression suites

Exact candidate head: 2b7afdb

Release hold

This remains draft until exact-head hosted checks and automatic Codex review are clean, PR #426 is explicitly dispositioned, the final installed-Codex #411 proof passes, all live bug/review inventories are clear, and the public v0.4.3 package/install/runtime/plugin/skill/CLI/MCP surfaces are verified. No issue is auto-closed by this PR body.