Support JSONC (JSON with comments) in settings.json

Problem

settings.json files grow complex as users add permission rules, hooks, plugins, and status line config. There's no way to document why a rule exists inline — you have to maintain a separate file or rely on a templating tool like chezmoi to keep comments in a source file that renders to plain JSON.

For example, a permission allow list with 20+ entries benefits from grouping and annotation:

{
  "permissions": {
    "allow": [
      // Read-only git commands (no destructive flags, no embedded interpreters)
      "Bash(git status)",
      "Bash(git log *)",
      "Bash(git diff *)",
      "Bash(git show *)",

      // CLI tools (read-only, no network)
      "Bash(jq:*)",
      "Bash(yq:*)",
      "Bash(bat:*)",

      // Project-specific tooling (pre-approved safe binaries)
      "Bash(terraform plan *)",
      "Bash(kubectl get *)"
    ]
  }
}

Without comments, the rationale for each group is lost. Users either under-document their security decisions or move to external tooling just to get comments.

Proposal

Parse settings.json (and settings.local.json) as JSONC — JSON with // and /* */ comments stripped before parsing. This is the same format VS Code uses for its settings.json, so the convention is well-established in the developer tools space.

No new file extension needed. Standard .json files that happen to contain comments just work. Files without comments continue to parse identically.

Alternatives considered

• Separate documentation file: Works but disconnects the explanation from the rule it describes.
• Chezmoi/templating: Effective but adds a build step and tooling dependency just to get comments.
• YAML or TOML config: Bigger migration, comments are just one benefit.