feat(cmd): add the encoder mode to the toml-test adapter

Assisted-by: DeepSeek V4.1 Flash

docs/ARCHITECTURE.md

@@ -7,9 +7,9 @@ source tree; nothing is aspirational.
 
 interpres is one public library package, one command, and one example. The
 library implements the whole of TOML 1.1, decoding and encoding, in the
-standard library alone; the command wraps the parser for the toml-test
-compliance harness, against which it stands at 214 valid and 467 invalid cases
-with zero failures; the example demonstrates the API.
+standard library alone; the command wraps the parser and the encoder for the
+toml-test compliance harness, against which it stands at 214 valid, 467 invalid
+and 214 encoder cases with zero failures; the example demonstrates the API.
 
 ```mermaid
 flowchart TD
@@ -36,7 +36,7 @@ strict validation.
 | Path | Responsibility |
 |---|---|
 | `.` (package `interpres`) | The whole library. `interpres.go` declares the exported surface (`Parse`, `Unmarshal`, `Marshal`, the `*Context` variants, `Decoder`, `Encoder`, `Marshaler`, `Unmarshaler`, `SyntaxError`, the local date-time types); everything below it is unexported. |
-| `cmd/interpres-decode` | The toml-test adapter. Reads TOML on stdin, writes tagged JSON on stdout. Owns no parsing logic. |
+| `cmd/interpres-decode` | The toml-test adapter, both directions. Reads TOML on stdin, writes tagged JSON on stdout; with `-encode` it reads tagged JSON and writes TOML. Owns no parsing logic and no emission logic. |
 | `examples/basic` | A runnable tour of the API. Documentation in executable form, not part of the library. |
 
 Inside the library package, one file owns one concern: