docs: add story and OpenClaw design foundations

[JOY (JOY)]

Summary

• Add story bible, demo lore direction, permanent NPC characteristic docs, and manhwa/Gate reference notes.
• Add OpenClaw agent connection architecture while preserving Nakama/Fusion/api.dos.ai authority boundaries.
• Add local Fusion dev build docs and helper scripts, plus a Unity editor build utility.
• Record the local worktree path rule in AGENTS.md, .claude/CLAUDE.md, and agent handoff docs.

Local review

• Local code-review fallback: APPROVED WITH SUGGESTIONS.
• No blockers found. Scope is docs plus local build tooling, with no gameplay authority changes.
• Suggestion: production dedicated server build remains a separate lane from this fast local client/host dev loop.

Tests

• npx --yes markdownlint-cli2@0.13.0 README.md ROADMAP.md CHANGELOG.md CONTRIBUTING.md SECURITY.md AGENTS.md .claude/CLAUDE.md "docs/**/*.md"
• git diff --cached --check before commit
• PowerShell parser check for tools/build-unity-windows-dev.ps1 and tools/launch-local-second-client.ps1
• dotnet build Unity/Assembly-CSharp-Editor.csproj --nologo (third-party Photon/Fusion warnings only, 0 errors)
• dotnet build Unity/SecondSpawn.AI.csproj --nologo
• dotnet build Unity/SecondSpawn.Networking.csproj --nologo
• dotnet build Unity/SecondSpawn.UI.csproj --nologo

Codex (@codex) please review this PR.

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