fix(tui)!: per-agent role models in workflow.yaml + canonical SDD preload

[davidarce]

Summary

• WorkflowRole.Model (single string) is replaced by WorkflowRole.Models map[string]string keyed by agent name (claude/opencode/copilot). Required for kind: subagent; rejected on kind: orchestrator.
• DevRune fetches SDD's workflow.yaml from the canonical catalog source (github:davidarce/devrune-starter-catalog) at wizard start via the existing cache layer, before the model-selection step. The synthetic hardcoded SDD role list is gone.
• Each renderer (claude / opencode / copilot) reads role.Models[agent] instead of role.Model. buildWorkflowPlaceholderReplacements gains an agentName parameter.

Why

The TUI model-selection step on a fresh install never received the yaml's declared model defaults. app.go passed an empty []WorkflowManifest to RunWorkflowModelSelection (model selection runs before the catalog scan by design), so the synthetic fallback in workflow_models.go:909-917 used Model: roleName placeholders instead of real values. Even when the user later saved choices to devrune.yaml, the catalog could only express one tier per role across all agents — not enough for "haiku on claude, claude-haiku-4.5 on opencode, Claude Haiku 4.5 on copilot".

Schema

roles:
  - name: sdd-explorer
    kind: subagent
    skill: sdd-explore
    models:
      claude: haiku
      opencode: haiku
      copilot: Claude Haiku 4.5

Architecture

internal/tui/scanner.go exposes FetchSDDWorkflow(ctx, cachePath) and the constant CanonicalSDDSource. app.go:115-133 calls it before invoking RunWorkflowModelSelection, passing the resulting manifest. The same fetch is performed again at the regular scan step but the cache layer makes it near-instant. Network failures fall through silently — the wizard continues with "inherit" defaults.

Breaking change

Catalogs that still declare model: instead of models: will fail Validate(). Requires the matching catalog update in davidarce/devrune-starter-catalog#53.

Test plan

• go test ./... (full suite)
• Unit tests added: TestSubagentRoles_FiltersByModelsMap, TestWorkflowRole_ValidateModelsRequired, TestWorkflowRole_ModelFor
• Manual: install SDD from scratch, verify model-selection step seeds per-agent defaults from the catalog
• Manual: re-run "manage sdd models" and verify saved selections still load
• Manual: install offline (no cache, no network) — wizard continues with "inherit" defaults

Closes #67

🤖 Generated with Claude Code