fix(web): redeploy and room join reuse the agent's source slug; roster shows the agent's name (CL-8522)

[TheGreatAxios]

Summary

• Restart on a not-running package-deployed agent (e.g. agent-echo-bot-source) was double-wrapping the asset name: deployAgentSource slugified the raw asset name and re-wrapped it, minting a new asset like agent-agent-echo-bot-source-source instead of reusing the existing one.
• NewAgentInput now takes an optional slug, used verbatim (validated) instead of re-deriving one from name. agentSlugFromSourceAssetName is the inverse of agentDeploySourceAssetName.
• redeployRoomAgent and the room-join loop in createWorkbench now derive the slug from the existing assetName and pass it through, so a restart or room join reuses the same asset.
• displayAgentName renders a non-Myra agent-<slug>-source asset as its title-cased slug ("Echo Bot") instead of the raw asset name.

Closes CL-8519.

Test plan

• bunx tsc -p apps/web --noEmit
• bun run lint
• bun run fmt
• cd apps/web && bun run build
• cd apps/web && bun test ./src (595 pass)

[linear-code]

CL-8522

CL-8519