feat: surface current session in recents and use repo-aware worktree names #77

Description

The current recent-session surfaces do not make the active/latest session feel obvious, and generated worktree names under the opencode data directory are still opaque adjective/noun names. This makes it harder to recognize the current conversation at a glance and harder to map temp worktrees back to the source repo.

Proposed Changes

• Make recent-session UI behave more like ChatGPT recents:
  • keep the latest/current session visibly at the top
  • show stronger session context on the row/card
  • include project/worktree context so random sandbox paths are understandable
• Change generated worktree names to include the source repo directory as a prefix, with a stable readable suffix (for example vibe-<timestamp> or equivalent unique form).

Acceptance Criteria

• Recent-session surfaces show the newest/current session first
• Recent-session rows/cards include readable project/worktree context
• New generated worktrees use the main repo directory name as a prefix
• Name generation still guarantees uniqueness and valid git branch names
• Relevant app/worktree tests pass locally