fix: surface NPC dialog response lifecycle

[JOY (JOY)]

Summary

• Add focused NPC response lifecycle callbacks from PrototypeAgentBrain to the UGUI chat panel.
• Show waiting/retry status while the NPC is contacting DOS.AI.
• Add a clear system line when a focused NPC exhausts bounded DOS.AI retry attempts.
• Update ROADMAP and CHANGELOG.

Local code review

Verdict: APPROVED WITH SUGGESTIONS.

Notes:

• No authority regression found. The lifecycle callbacks only update local UI state.
• No client key exposure found.
• Suggestion for a later PR: migrate the legacy IMGUI chat debug panel or remove it once UGUI is fully accepted. The new system lifecycle line is only rendered by UGUI, which is the default panel.

Verification

• npm.cmd install in backend/nakama
• npm.cmd run build in backend/nakama
• npm.cmd test in backend/nakama
• dotnet build Unity\SecondSpawn.AI.csproj
• dotnet build Unity\SecondSpawn.UI.csproj
• npx.cmd markdownlint-cli2 ROADMAP.md CHANGELOG.md
• git diff --check
• em dash scan on changed files