fix(tui): scope Zed editor context to containing workspaces

[kitlangton]

Summary

• Prevent Zed DB fallback from using editor context from workspaces nested inside the OpenCode session directory
• Prefer the most-specific containing Zed workspace when multiple ancestor workspaces match
• Skip inaccessible Zed DB candidates instead of crashing in sandboxed CLI runs
• Add regression coverage for containing, most-specific, nested workspace, and inaccessible DB path cases

Fixes #25164

Testing

• bun test test/cli/tui/editor-context-zed.test.ts
• bun typecheck
• git push hook: bun turbo typecheck