[FEATURE]: Smart auto-upgrade based on installation method #23435

Describe the enhancement you want to request

Problem

When OpenCode is installed via local npm install (e.g., npm install opencode-ai without -g flag, common on shared servers where users lack sudo access), the auto-upgrade mechanism fails:

1. TUI shows upgrade prompt: "A new version is available"
2. User clicks "Update" button
3. Upgrade fails with permission error (tries to write to /usr/local/lib)
4. No fallback or guidance for local install scenarios

Current Behavior

The opencode upgrade command assumes global installation:

• Attempts npm install -g → requires sudo
• Or attempts curl download to /usr/local/bin → requires sudo
• Fails silently without detecting local install context

Proposed Enhancement

Smart upgrade detection: Automatically detect the installation method and use the appropriate upgrade strategy:

Implementation Suggestions

1. Detect install location by checking:

   • process.execPath or __dirname of the running binary
   • If path contains node_modules/opencode-ai, it's a local npm install

2. For local npm installs, run:

   cd <install-dir>/node_modules/opencode-ai/../..
   npm install opencode-ai@latest

3. Show informative error if upgrade still fails, with manual workaround instructions

Benefits

• Users on shared servers (no sudo) can use auto-upgrade
• Reduces confusion about "upgrade failed" errors
• Better UX for non-global installation scenarios
• Consistent behavior across all installation methods

Workaround (Current)

Users must manually run:

cd /path/to/node_modules/opencode-ai/../..
npm install opencode-ai@latest