fix(worktree): handle historical session toggles

[bobleer]

Summary

• locate view-only persisted sessions by their owning project and restore empty sessions before rebinding
• reject sessions with history or active processing at the final session mutation lock, with safe worktree rollback
• serialize each complete session binding transition so concurrent callers cannot create competing worktrees
• keep the desktop toggle synchronized after historical hydration and coalesce repeated clicks
• preserve structured worktree errors so the UI never renders [object Object]
• apply the same history guard and project locator in CLI, and accept Windows-style home-relative worktree roots

This is a follow-up to #1815.

Verification

• cargo test -p bitfun-core execution_binding --lib
• cargo test -p bitfun-core service::worktree --lib
• cargo test -p bitfun-cli worktree --bin bitfun
• cargo test -p bitfun-services-integrations --features git git::managed_worktree::tests --lib
• cargo check --workspace
• cargo check -p bitfun-desktop
• pnpm run lint:web
• pnpm run type-check:web
• focused Vitest suite: 26 tests
• pnpm run check:repo-hygiene