auto_install_extensions fails on JSONC comments and trailing commas

[rodmk]

Module: code-server and vscode-web (latest)

Expected: auto_install_extensions = true parses .vscode/extensions.json with comments and trailing commas (valid JSONC).

Actual: The sed 's|//.*||g' | jq pipeline fails on:

• /* */ block comments — sed only strips //
• Trailing commas — jq rejects them
• URLs in strings — sed mangles https:// to https:

Reproduction: Create .vscode/extensions.json:

{
  "recommendations": [
    "ms-python.python",
    /* a block comment */
    "dbaeumer.vscode-eslint", // trailing comma
  ]
}

Use auto_install_extensions = true — extensions fail to install.

Fix in #707.

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