feat: add --resume flag to interactively select session

[yanmxa]

Summary

Adds a --resume (-r) flag to the run command. When used, it fetches available sessions and presents an interactive list (using @clack/prompts) for the user to select one to resume.

This mimics the behavior of claude code --resume.

Changes

• Modified packages/opencode/src/cli/cmd/run.ts to add resume option and handling logic.
• Uses Locale.todayTimeOrDateTime for friendly timestamps.
• Filters out sub-sessions (sessions with parentID).

Testing

• Verified opencode run --help shows the new flag.
• Verified typecheck passes.

Closes #2404