feat(cli/sdk/mcp): expose per-launch agent models

[Shravankb301]

Summary

• add --model <id> to superset agents create and superset workspaces create
• forward per-launch model selection through the TypeScript SDK
• expose the host's existing model and effort inputs in MCP agent and workspace launch tools
• document the new CLI, SDK, and MCP surface

Why

The host service has supported per-launch model selection since #5248, using
the shared per-agent model registry to translate a model ID into the correct
flag or environment variable. Desktop can already use that path, but CLI, SDK,
and MCP callers cannot.

This change exposes the existing host behavior without duplicating model maps
or changing launch semantics. Omitting model still delegates to the agent's
configured default.

This is a focused first slice of #5202. Agent-config CRUD and arbitrary
command/environment overrides remain out of scope.

CLI surface

$ superset agents create --help
  --model <string>  Model for this launch (agent-specific; omit to use the agent default)

$ superset workspaces create --help
  --model <string>  Model for the spawned agent (agent-specific; omit to use the agent default)

workspaces create --model requires --agent, matching the existing
--effort contract.

Testing

• bun test packages/cli/src/commands/agents/create/command.test.ts packages/cli/src/commands/workspaces/create/command.test.ts — 9 passed
• bun run typecheck — 37/37 tasks passed
• bun run lint — 6,189 files checked, no fixes
• bun run --filter @superset/cli build — passed
• bun run --filter @superset/sdk build — passed
• compiled CLI help confirms --model on both launch commands

The full bun run test gate reached the desktop suite with 2,798 passing and
one unrelated environment-sensitive failure in
getProcessEnvWithShellPath applies shell PATH: this machine adds
/usr/local/sbin to the returned macOS process path, while the existing test
expects exact equality with the login-shell path. The same focused test fails
in isolation, and none of this PR's files touch shell environment handling.

Related issue

Progresses #5202.

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Summary by cubic

Expose per-launch agent model selection in @superset/cli, @superset/sdk, and @superset/mcp so callers can choose a model per run. Previously only the host/Desktop path supported per-launch models; other surfaces always used the agent default. Omitting model still uses the agent’s default. Progresses #5202.

• CLI: Add --model to superset agents create and superset workspaces create; require --agent when using --model; forward to host; tests and help updated.
• SDK: Add optional model to agents.create and WorkspaceAgentLaunch; forward to host; docs and api.md updated; no breaking changes.
• MCP: Add optional model (and expose effort) in agents_create and workspaces_create tools; schema and docs updated.

^{Written for commit 923fc25. Summary will update on new commits.}