docs: update AGENTS.md for parser/ submodule layout

AGENTS.md

@@ -3,8 +3,16 @@
 ## Project Structure & Module Organization
 - `src/main.rs`: Entry point; wires CLI to parser.
 - `src/cli.rs`: Clap-based argument parsing (flags like `--file`, `--input-format`).
-- `src/parser.rs`: DER decoding and pretty-printing using `yasna`.
 - `src/color.rs`: Minimal ANSI color helpers.
+- `src/parser/`: Parser submodule containing all DER decoding and pretty-printing logic.
+  - `mod.rs`: Public API surface for the parser (re-exports types and `pretty_print_der`, `parse_and_print`).
+  - `asn1_types.rs`: TLV parsing, OID decode, helpers.
+  - `encoding_utils.rs`: Hex/bits formatting utilities and truncation logic.
+  - `pretty_printer.rs`: Recursive DER walker and structure rendering.
+  - `value_printer.rs`: Leaf value formatting (strings, times, OIDs, bit/octet strings).
+  - `certificate_utils.rs`: X.509-specific helpers and detection.
+  - `time_utils.rs`: UTCTime/GeneralizedTime humanization.
+  - `oid_registry.rs`: Friendly OID names.
 - `tests/data/`: Sample keys/certs used by integration tests or manual runs.
 - `Cargo.toml`: Rust 2021 package config and dependencies.
 
@@ -24,12 +32,12 @@
 ## Coding Style & Naming Conventions
 - Rust 2021; 4-space indent; `rustfmt` defaults (`cargo fmt`).
 - Naming: modules `snake_case`; types/enums `CamelCase`; functions `snake_case`; constants `SCREAMING_SNAKE_CASE`.
-- Avoid `unsafe`; prefer clear, small functions. Keep CLI parsing in `cli.rs`, decoding/formatting in `parser.rs`.
+- Avoid `unsafe`; prefer clear, small functions. Keep CLI parsing in `cli.rs`, decoding/formatting in `src/parser/`.
 - Run `cargo clippy` locally and fix lints before PRs.
 
 ## Testing Guidelines
 - Framework: built-in Rust tests (`cargo test`).
-- Unit tests: add `#[cfg(test)] mod tests { ... }` near code in `parser.rs`.
+- Unit tests: add `#[cfg(test)] mod tests { ... }` near code in the relevant file under `src/parser/`.
 - Integration tests: create Rust files under `tests/` (e.g., `tests/parse_certificate.rs`) and use fixtures in `tests/data/`.
 - Naming: prefer descriptive test names (e.g., `it_parses_bit_string_flags`).
 - If output formats change, update or add tests that assert on rendered lines.