zg install --target opencode fails on JSONC configs (comments in opencode.json) #97

Describe the bug

zg install --target opencode throws Invalid JSON when the existing
~/.config/opencode/opencode.json contains // comments (JSONC).

To reproduce

1. Create ~/.config/opencode/opencode.json with a comment (opencode
   officially supports JSONC; configs it manages commonly carry comments):

   {
    // "model": "some-model", // e.g. a commented-out model line
    "mcp": {}
   }

2. Run zg install --target opencode --yes

Actual result

Error: Invalid JSON in /home/<user>/.config/opencode/opencode.json.
Cause: Expected double-quoted property name in JSON at position ...

Expected result

zg merges its managed zvec_grep MCP entry into the existing config while
preserving the user's comments and unrelated keys.

Root cause (from source)

src/cli/install.ts — parseJsonObject() uses strict JSON.parse. The file
already imports parse from jsonc-parser, but it is only used on the Qoder
path (parseJsoncSettings); the OpenCode (and other mcpServers container)
paths parse with plain JSON.parse.

Suggested fix

Parse agent config files with jsonc-parser everywhere. If the managed entry
is written back with JSON.stringify, also keep the comments — e.g. use a
comment-preserving editor (jsonc-parser's modify/applyEdits or similar) so
the user's commented-out settings survive the install. Uninstall
(uninstallJsonMcpServer) has the same read problem and should be covered
too.

Environment

• zvec-grep: 0.2.1
• Node: v24
• OS: Linux