(release) v1.8.0 prep: docs sweep, roadmap cleanup and version bump

[krissen]

Summary

Release preparation for v1.8.0 (the navigation-overhaul series #235–#245).

• ROADMAP: logged the inherited parked-tab empty-detection edge ((workflowbar-autohide) Floating pill styling and welcome/empty-state autohide gate #245 review note) and a pre-existing Cmd+Shift+L accelerator collision (Lightroom vs reset-layout); removed the navigation series' completed items; date bumped.
• Docs sweep vs the post-series end state: architecture.md (declarative module catalog, workflow specs, morph engine, command router + launch handshake) and CLAUDE.md (flexlayout file list, CLI routing chain) updated; workspace-guide/ux-principles/README verified already current.
• Release prep per release-guide step 1: [Unreleased] → [1.8.0] - 2026-07-18, version bumped to 1.8.0 in frontend/package.json, backend/pyproject.toml and backend/api/server.py.

Testing

• npm test: 91 files / 886 tests passed
• npm run build:workspace: OK