templates: add versioned reusable agent-team Partituras

[guicybercode]

Context

Teams repeatedly use the same arrangements: architect, developer, reviewer, tester, notes, and communication links. Rebuilding the topology for every task is slow and error-prone.

Goal

Add reusable, versioned Agent Team templates, inspired by Partituras, that can instantiate a task team with roles, connections, notes, and layout hints.

Scope

• Define a versioned template schema.
• Include role references, adapter capability requirements, connection types, starter notes, and optional canvas positions.
• Support local create, duplicate, edit, archive, import, and export.
• Validate templates before task side effects.
• Resolve agents and roles through stable IDs or portable selectors.
• Provide a preview showing missing capabilities and substitutions.

Acceptance criteria

• Exported templates contain no env values, secrets, machine-specific absolute paths, session IDs, or PTY data.
• Unknown future fields can be preserved or rejected according to the schema version.
• Instantiation is all-or-nothing before worktree/session creation begins.
• Missing agents do not silently select a different vendor.
• Users explicitly approve substitutions.
• Historical tasks retain the template version they used.
• Import rejects malformed, oversized, and cyclic connection graphs.
• Round-trip and migration tests cover at least two schema versions.

Out of scope

A public template marketplace and cloud synchronization.