fix: show git worktrees as selectable projects

[Fr4nzz]

Summary

• Git worktrees are currently filtered out of the project list by isLinkedGitWorktree(), making them invisible to the bot
• Users working in worktrees cannot access their sessions — /projects doesn't list them and /open fails when navigating to a worktree directory
• OpenCode stores worktree paths in the project's sandboxes field and supports listing sessions by worktree directory, but the bot ignores both

Changes

• Remove the worktree exclusion filter in getProjects()
• Include worktree paths from the sandboxes field returned by the OpenCode project API
• Worktrees now appear as independent selectable projects with their own session histories
• Remove the now-unused isLinkedGitWorktree() function and its fs/path imports

How to reproduce the bug

1. Create a git worktree: git worktree add ../my-project-feature
2. Open OpenCode in the worktree directory and create sessions
3. Start the Telegram bot and run /projects — the worktree doesn't appear
4. Try /open and navigate to the worktree — fails with "could not add project"

After this fix

• /projects lists worktrees alongside regular projects
• /open successfully adds worktree directories
• /sessions shows sessions created in the worktree

Test plan

• Tested on ARM64 Ubuntu with git worktree of an existing repo
• /projects shows both parent repo and worktree
• /sessions lists worktree-specific sessions
• /open can navigate to and select a worktree directory
• Build passes with zero errors

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