Summary

• Render [lsp] and [lsp.servers.<lang>] in RenderTOMLForScope so SaveTo preserves user LSP overrides.
• Sort LSP server keys and quote non-bare language ids such as c++ for deterministic, valid TOML.
• Add round-trip coverage for full, user, and project scoped renders.

Root cause

Config.LSP was loaded correctly, but the annotated TOML renderer never serialized it back out. Any save operation rewrote the config without the LSP section.

Validation

• go test ./internal/config -count=1
• go test ./internal/config -run ^$ -bench BenchmarkRenderTOMLWithLSPServers -benchmem -count=5
  • 64-server render: 132-153 us/op on Windows amd64 / i9-12900H
• go vet ./...
• go test ./... -p 1 -count=1
  • Local Windows note: all reached non-CLI packages passed; internal/cli/TestACPFactoryLoadsSessionCwdProjectConfig still fails at TempDir cleanup with a file-in-use error outside this render path.
• go test ./desktop/... -count=1
  • Local Windows note: unrelated desktop failures were observed in TempDir cleanup, skill path restoration, and escaped filename handling.

Closes #3464