[AmitKulkarni23]

The JSONC fallback converts each UTF-8 byte into a separate character, so installing MCP into a commented config changes existing keys and values such as café to café.

Keep the original bytes while stripping comments and trailing commas, then convert the result back to UTF-8. Add regression coverage for Unicode keys and values, escaped strings, line and block comments, and trailing commas. Exercise all seven JSON-based MCP targets with each transport and verify that malformed configs remain unchanged.

Validation on macOS:

• Both Unicode regressions fail before the fix and pass afterward.
• cargo test --locked: 1,862 unit tests and 30 integration tests passed; six existing tests ignored. The suite required an unrestricted run because the sandbox blocks ps in the OpenCode lifecycle test.
• cargo check --locked
• cargo clippy --locked --all-targets --all-features (existing repository warnings)
• cargo fmt --all -- --check
• Ran the reported OpenCode fixture, a strict JSON control, and a block-comment variant through the compiled CLI in disposable homes; existing Unicode entries survived and the Railway entry was installed.

Closes #1312