fix(app): preserve workspace terminals across session routes

[CannonRS]

Issue for this PR

Closes #48531

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Moves the workspace-terminal cache from route scope to app scope so terminals survive session-route changes.

Previously TerminalProvider (mounted in the session page) created a per-route cache and disposed all its terminal sessions when the route unmounted. Switching chats in the same workspace directory therefore tore down an open bottom terminal. This PR introduces an app-level TerminalRegistryProvider that owns a createWorkspaceTerminalRegistry (LRU with the same MAX_TERMINAL_SESSIONS limit) and makes TerminalProvider resolve its workspace sessions through that registry instead of a route-local map. The draft page also mounts TerminalProvider so a new chat can reopen the same bottom terminal before its first prompt.

How did you verify your code works?

• bun typecheck (tsgo) passes in packages/app.
• terminal.test.ts passes 8/8, including two new tests for createWorkspaceTerminalRegistry (reuse across same key, LRU eviction with per-workspace separation).
• git diff --check clean; no unrelated changes.

Screenshots / recordings

n/a (behaviour fix; no visual change)

Fork

• Source fork: https://github.com/mQorva/OpenCode
• Diff against this fork's dev: mQorva/OpenCode@dev...workspace-terminals
• mQorva issue / context: n/a

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR