fix(console): allow owners to edit agent settings and add model field (#2630)

## Summary

**1. Owner edit permission fix**

`AgentSettingsForm` gates the whole form behind `tierForCurrentUser ===
'EDIT'` (`canEdit = !isGlobal && tier === 'EDIT'`), but the aistio agent
API never populates `tierForCurrentUser`. Result: **every** user agent's
settings page is read-only in the console — name/description/system
prompt etc. cannot be edited from the UI, only via raw API.

Fix: treat the agent owner as EDIT-capable (`agent.ownerId ===
getUsername()`), keeping the tier check for non-owners.
`tierForCurrentUser` remains honored when the backend eventually
provides it.

**2. Model field in create + settings forms**

The backend (`POST /api/agents`, `PUT /api/agents/:id` →
`agentCreateReq.model`) has always accepted a `model`, but neither
`AgentCreatePage` nor `AgentSettingsForm` exposed it. Added a Model
input to both forms so provider-qualified ids like
`deepseek:deepseek-chat` / `openai:gpt-4o` are configurable from the
console. Empty falls back to the data-plane default model.