Wire up status-in-dev label and PR-merge automation

[vybe]

Context

The SDLC (Todo → In Progress → Review → Done) has a gap: when a PR merges to dev, the issue stays status-in-progress until the release cut to main auto-closes it. There's no visible "merged to dev, awaiting release" state.

The board already has an In Dev column (added previously but unused — nothing populates it). Since workflow is driven from gh issue list, labels are the right surface.

What this delivers

• New label: status-in-dev
• New GH Action .github/workflows/issue-status-on-merge.yml: on PR merge to dev, parse Fixes/Closes/Resolves #N from PR body+title, stamp status-in-dev, strip status-in-progress
• /release skill updated: use gh issue list --label status-in-dev as the authoritative "what's shipping" list for release notes; include Closes #N in the release PR body so issues auto-close when merged to main
• DEVELOPMENT_WORKFLOW.md updated: 4-stage SDLC becomes Todo → In Progress → In Dev → Done, with 1:1 mapping to commit-graph location

Result

Todo → In Progress → In Dev (on origin/dev) → Done (on origin/main, closed)
(none)  (in-progress)  (in-dev)                (no label, issue closed)

Out of scope

• Project board automation (user works from gh issue list, not the board)
• status-review label decision (currently exists but unused — leave for follow-up)