fix(app): restore recently-used models display and project labels in recent sessions

[OpenCodeEngineer]

Problem

After rebasing on upstream/dev, two webapp UI features are broken/missing:

1. Recently used models not visible

The model context (packages/app/src/context/models.tsx) stores and persists recently used models, and local.tsx exposes model.recent — but these aren't surfaced in the sidebar recent panel or model picker in a discoverable way. The models are only available via cycling (keybind) but not shown visually.

2. Missing project name/workspace labels in recent sessions sidebar

The sidebar recent panel (packages/app/src/pages/layout/sidebar-recent.tsx) shows session titles grouped by time, but does not display the project/workspace path label for each session. The recentPrefix() utility already exists in packages/app/src/utils/recent-session.ts and is used in the full recent page (pages/recent.tsx) but is not referenced from the sidebar panel's <SessionItem> rendering.

Plan

1. Recent sessions sidebar: Add project/workspace name label to session items in the sidebar recent panel — show recentPrefix(session) as a secondary line or tag so users can tell which workspace a session belongs to.

2. Recently used models: Surface recently used models in the model selector / prompt area so they're visually discoverable (not just cycleable via keybind).

Files to modify

• packages/app/src/pages/layout/sidebar-recent.tsx — add project label rendering
• packages/app/src/pages/layout/sidebar-items.tsx — optionally accept and render project label in SessionItem
• packages/app/src/components/dialog-select-model.tsx or prompt-input model controls — add recent models display

[OpenCodeEngineer]

All three features restored in branch fix/recent-models-and-labels:

1. ✅ Recently Used models group in model picker
2. ✅ Project/workspace labels in recent sessions sidebar
3. ✅ Collapsible parent/child session tree with hover preview

PR: OpenCodeEngineer#1

Also added FORK.md documenting fork-specific features and a rebase survival checklist to prevent this from happening again.