[codex] Create workspace sessions per font window

[kostyafarber]

Summary

Creates explicit main-process workspace sessions for font windows. Launcher windows now stay unbound, while each workspace window is attached to a WorkspaceSession that owns its own utility process, document client, document workflow, and attached renderer windows.

Motivation

This removes the previous renderer-carried workspace binding shape and the singleton workspace process. Main now resolves workspace and document connections from the sender window, which makes the invariant clearer: workspace windows are born attached to a workspace, and launcher windows do not connect to workspace data.

Changes

• Adds WindowManager, WorkspaceManager, and main-side WorkspaceSession.
• Moves WorkspaceProcess, DocumentClient, and DocumentSession ownership into each workspace session.
• Removes workspace.initialBinding and renderer-passed workspace ids.
• Makes workspace.connect() and document.connect() sender-scoped no-arg calls.
• Splits launcher and workspace routes: main loads /launcher for launcher windows and /home for workspace windows.
• Updates Create/Open to create a workspace session, open a bound workspace window, and close the launcher only when the opener is unbound.
• Keeps save/close lifecycle scoped to the relevant workspace session.

Validation

• pnpm --dir apps/desktop typecheck
• pnpm --dir apps/desktop exec oxlint --deny-warnings src/main src/renderer/renderer.ts src/renderer/src/app/Screens.tsx src/renderer/src/store/appStore.ts src/renderer/src/views/Landing.tsx src/renderer/src/lib/workspace src/shared src/utility/workspace/WorkspaceHost.ts src/utility/workspace/WorkspaceHost.test.ts
• pnpm --dir apps/desktop test
• Commit hooks: oxfmt, oxlint, tsgo typecheck, deadcode, vitest