[FEATURE] Add just recipe for GitHub issue and PR dashboard

[gerchowl]

Description

Add a just gh-issues recipe that displays open GitHub issues grouped by milestone in a rich, color-coded table, along with open pull requests. Provides a quick terminal-based project dashboard without leaving the CLI. Ships to all downstream workspaces via the sync manifest.

Problem Statement

There's no quick way to get an at-a-glance overview of open issues grouped by milestone, with structured columns for type, priority, scope, effort, semver impact, assignee, and linked branch — all from the terminal.

Proposed Solution

• New justfile.gh with a gh-issues recipe under a [github] group
• Python script scripts/gh_issues.py using rich tables for formatted output
• Issues grouped by milestone, each as a table with columns: #, Type, Title, Assignee, Branch, Prio, Scope, Effort, SemVer
• Linked development branches fetched in a single GraphQL call
• Open PRs in a separate section with: #, Title, Author, Branch, Review status, Delta
• Sync manifest entries to ship both files to downstream workspaces (.devcontainer/justfile.gh + .devcontainer/scripts/gh_issues.py)
• Downstream justfile template updated to import .devcontainer/justfile.gh

Alternatives Considered

• Pure bash with printf — alignment breaks on long titles
• gh issue list --json + jq — flat output, no grouping or color

Impact

• All downstream projects benefit from the dashboard out of the box
• No breaking changes, purely additive

Changelog Category

Added

[gerchowl]

Implementation Plan (retroactive)

Issue: #84
Branch: feature/67-declarative-sync-manifest (bundled with #67 work)

Tasks

• Task 1: Create justfile.gh with gh-issues recipe under [github] group — justfile.gh — verify: just gh-issues
• Task 2: Create scripts/gh_issues.py with rich table rendering for issues grouped by milestone — scripts/gh_issues.py — verify: uv run python scripts/gh_issues.py
• Task 3: Import justfile.gh from root justfile — justfile — verify: just --list shows [github] group
• Task 4: Add PR section to scripts/gh_issues.py with author, branch, review status, delta — scripts/gh_issues.py — verify: just gh-issues shows PR table
• Task 5: Add linked branch column via GraphQL batch query — scripts/gh_issues.py — verify: issues with linked branches show branch name
• Task 6: Use source_directory() in justfile.gh for portable script path resolution — justfile.gh — verify: just --evaluate _gh_scripts
• Task 7: Add sync manifest entries for justfile.gh → .devcontainer/justfile.gh and scripts/gh_issues.py → .devcontainer/scripts/gh_issues.py — scripts/sync_manifest.py — verify: just sync-workspace
• Task 8: Update downstream workspace justfile to import .devcontainer/justfile.gh — assets/workspace/justfile — verify: synced file includes import
• Task 9: Update CHANGELOG.md with [FEATURE] Add just recipe for GitHub issue and PR dashboard #84 entry under Added — CHANGELOG.md

Notes

• TDD skipped: non-testable change (CLI tooling, templates, config). Script has no unit-testable logic beyond subprocess calls and rich rendering.
• scripts/gh_issues.py depends on rich (transitive via bandit), gh CLI, and GitHub API access.