Fix Buzz command migration for saved agents

[wesbillman]

Summary

Fix saved agent startup after the Sprout→Buzz rename by repairing persisted built-in command/runtime values on desktop startup.

• Rewrite exact legacy managed-agent commands: sprout-acp → buzz-acp, sprout-agent → buzz-agent, and sprout-dev-mcp → buzz-dev-mcp.
• Rewrite removed MCP server values (sprout-mcp, sprout-mcp-server, buzz-mcp-server) to buzz-dev-mcp for Buzz agents, or clear them for non-Buzz agents.
• Rewrite persisted persona runtimes from sprout-agent to buzz-agent, including installed team .persona.md files so team sync cannot reintroduce the old runtime.
• Run the command repair after provider→runtime migration and before existing MCP reconciliation/team persona sync.

Adversarial Review

• Existing ManagedAgentRecord launch uses saved acp_command, agent_command, and mcp_command directly, so changing defaults alone would not fix existing agents.
• Manually changing only acp_command explains the follow-up os error 2: the saved agent_command can still be sprout-agent.
• personas.json can persist runtime: "sprout-agent"; future deploys from those personas could recreate broken managed-agent records.
• Installed team persona files can sync back into personas.json, so repairing only JSON stores would be non-durable.
• Custom commands and explicit paths are left untouched; only exact legacy built-in command names are rewritten.

Tests

• cargo fmt --manifest-path desktop/src-tauri/Cargo.toml
• cargo test --manifest-path desktop/src-tauri/Cargo.toml reconcile_legacy_command_names
• cargo test --manifest-path desktop/src-tauri/Cargo.toml rewrite_legacy_persona_md_runtime
• cargo test --manifest-path desktop/src-tauri/Cargo.toml reconcile_legacy_team_persona_runtime_files
• cargo test --manifest-path desktop/src-tauri/Cargo.toml reconcile_mcp_commands
• git diff --check
• Pre-commit hook: rust fmt, desktop/web fix + file sizes, mobile format/analyze
• Pre-push hook: desktop JS tests, desktop Tauri tests, mobile tests, desktop Tauri clippy, workspace clippy, rust unit tests