docs: sync roadmap tasks with issues

[JOY (JOY)]

Summary

• Create and link roadmap umbrella issues Track alpha demo implementation umbrella #260-Track post-alpha and beta roadmap decomposition #265 for alpha implementation, gameplay ledgers, NPC voice, Unity experiments, Bonebound future design, and post-alpha/beta decomposition.
• Add issue references to previously untracked ROADMAP checkboxes so backlog sync has a concrete GitHub handle for each actionable item.
• Document the scanned-doc color-token rule and adjust inventory color token text that the sync script could misread as issue references.

Local reviewer fallback

• Docs/config-only change reviewed manually against second-spawn-backlog and code-review skill requirements.
• No Unity, Nakama runtime, client, scene, prefab, package, or backend code changed.
• ROADMAP remains a public snapshot; GitHub issues remain the execution handles.

Verification

• tools\windows\check-backlog-sync.ps1
• npx.cmd --yes markdownlint-cli2 ROADMAP.md docs/design/45-inventory-and-equipment-system.md docs/setup/github-project-tracking.md
• git diff --check
• rg -n "—|–" ROADMAP.md docs/design/45-inventory-and-equipment-system.md docs/setup/github-project-tracking.md returned no matches.