Add work-system statusline segment

[gering]

Summary

• New /work-system:statusline skill renders a compact [ws ○… ●… ◇… ✓…] task-backlog segment in Claude Code's status line, mirroring the knowledge-system /statusline pattern.
• Counts the repo's tasks/*.md by state — ○ not-started, ● active (worktree), ◇ in review (open PR), ✓ merged (ready to /close) — with muted single-width glyphs; zero columns dropped.
• PR state comes from a short-TTL cache in .git/ refreshed by a detached background gh call, so a render never blocks on the network.
• Owns its own marker segment and coexists with the knowledge-system [cks …] block in one ~/.claude/statusline.sh (verified live).

Changes

• plugins/work-system/scripts/ws-statusline.sh — self-contained renderer (glyph mapping, worktree/PR state, background cache with a mkdir lock + stale-lock sweep).
• plugins/work-system/scripts/ws-statusline-install.sh — installer cloned from statusline-install.sh: own # {{ws}} marker, atomic + restorable install/enable/disable/uninstall/status.
• plugins/work-system/skills/statusline/SKILL.md — thin wrapper over the installer.
• Version bump work-system 1.6.0 → 1.7.0; READMEs, CLAUDE.md, CHANGELOG.md, and the statusline knowledge entry updated.

Readiness

• ✅ README (top-level + work-system) updated
• ✅ Version synced (plugin.json + marketplace.json)
• ✅ CHANGELOG entry added
• ✅ Knowledge entry updated (statusline-integration.md)
• ✅ check-structure.py green (0 errors)
• ➖ Build N/A (declarative markdown plugins)

Test plan

• bash "$HOME/.claude/plugins/.../ws-statusline.sh" <repo-with-tasks> renders [ws …]; silent outside a tasks/ backlog.
• install injects the # {{ws}} block alongside an existing [cks …] block without touching it; uninstall strips it cleanly.
• All four state columns render (○ ● ◇ ✓) and zero columns are dropped.

🤖 Generated with Claude Code