refactor: build system auto-discovery, updated docs

- build.rs discovers boards by content (implements LoRaBoard), not exclusion lists
- build.rs auto-discovers helper modules by scanning board files for use super::<helper>
- Jinja template dynamically generates cfg gates for helpers
- Updated PORTING.md for new architecture (hal/, driver/, BoardParts, associated types)
- Zero manual template editing needed when adding boards to existing MCU families

src/board/PORTING.md

@@ -5,14 +5,14 @@
 ### 1. Create the board file
 
 Create `src/board/your_board.rs`. Use an existing board as a template:
-- ESP32-S3 boards: copy `heltec_v4.rs` (uses shared helpers from `esp32s3.rs`)
-- nRF52840 boards: copy `rak_wisblock_4631.rs`
+- ESP32-S3 boards: copy `heltec_v4.rs` (uses shared helpers from `board/esp32s3.rs` and `hal/esp32s3.rs`)
+- nRF52840 boards: copy `rak_wisblock_4631.rs` (uses shared helpers from `hal/nrf52840.rs`)
+- New MCU family: create a new `hal/<mcu>.rs` with MCU primitives first
 
-ESP32-S3 boards share common type aliases, peripheral bundles, and init helpers
-via `src/board/esp32s3.rs`. Your board file only needs the trait impl and
-board-specific init (Vext GPIO, display reset). If you add a new ESP32-S3 board,
-add its feature to the `#[cfg(any(...))]` gate on `mod esp32s3` in
-`src/board/mod.rs.j2`.
+`build.rs` auto-discovers your board file — any `.rs` file in `src/board/` that
+implements `LoRaBoard for Board` is automatically detected as a board. Helper
+modules (like `esp32s3.rs`) are auto-discovered via `use super::<helper>` imports
+in board files. No template editing or exclusion lists needed.
 
 ### 2. Define concrete types
 
@@ -21,7 +21,9 @@ Your board must export these type aliases:
 ```rust
 pub type RadioDriver = ...; // Must work with lora_phy::LoRa<RadioDriver, Delay>
 pub type UsbDriver = ...;   // Must implement embassy_usb_driver::Driver<'static>
+                             // (or UartDriver for UART boards)
 pub type DisplayI2c = ...;  // Must implement embedded_hal_async::i2c::I2c
+pub type DisplayDriver = ...; // Must implement DrawTarget<Color = BinaryColor>
 ```
 
 ### 3. Define peripheral bundles
@@ -32,39 +34,43 @@ pub struct RadioParts {
     pub delay: embassy_time::Delay,
 }
 
-pub struct UsbParts {
+pub struct UsbParts {  // or UartParts for UART boards
     pub driver: UsbDriver,
 }
 
 pub struct DisplayParts {
     pub i2c: DisplayI2c,
-    pub mac: [u8; 6],
 }
 ```
 
 ### 4. Implement the LoRaBoard trait
 
 ```rust
-use super::traits::LoRaBoard;
+use super::traits::{BoardParts, LoRaBoard};
 
 impl LoRaBoard for Board {
     const NAME: &'static str = "Your Board Name";
     const TX_POWER_RANGE: (i8, i8) = (-9, 22); // check your radio + PA
+
+    type RadioParts = RadioParts;
+    type CommParts = UsbParts;       // or UartParts
+    type DisplayParts = DisplayParts;
+    type DisplayDriver = DisplayDriver;
+
     fn init() -> Self { ... }
     fn mac_address() -> [u8; 6] { ... } // read from efuse, FICR, etc.
+    fn into_parts(self) -> BoardParts<RadioParts, UsbParts, DisplayParts> {
+        // Initialize buses via hal::, construct drivers, return BoardParts
+        BoardParts { radio, host, display: Some(display_parts), mac: Self::mac_address() }
+    }
 }
 ```
 
-The compiler will refuse to build if any of these are missing.
-
-### 5. Implement `Board::into_parts()`
+### 5. Add display init
 
 ```rust
-impl Board {
-    pub fn into_parts(self) -> (RadioParts, UsbParts, Option<DisplayParts>) {
-        // Initialize SPI, DMA, radio, USB, I2C
-        // Return peripheral bundles
-    }
+pub async fn create_display(i2c: DisplayI2c) -> Option<DisplayDriver> {
+    // Construct and initialize your display driver (SSD1306, SH1106, etc.)
 }
 ```
 
@@ -79,7 +85,7 @@ your_board = ["dep:your-hal", ...]
 
 ### 7. Add to justfile
 
-Add your board's feature/target/chip to the `boards` list at the top of `justfile`.
+Add your board's feature/target/chip to the board definitions at the top of `justfile`.
 
 ### 8. Build and test
 
@@ -88,5 +94,3 @@ just check your_board    # Must compile
 just clippy your_board   # Must be clean
 just build your_board    # Produces firmware
 ```
-
-`build.rs` auto-discovers your `.rs` file — no template editing needed.

src/board/mod.rs.j2

@@ -2,9 +2,10 @@
 pub mod traits;
 pub use traits::*;
 
-#[cfg(any(feature = "heltec_v3", feature = "heltec_v4"))]
-mod esp32s3;
-
+{% for helper, helper_features in helpers|items -%}
+#[cfg(any({% for f in helper_features %}feature = "{{ f }}"{% if not loop.last %}, {% endif %}{% endfor %}))]
+mod {{ helper }};
+{% endfor %}
 cfg_if::cfg_if! {
     {%- for board in boards %}
     {% if loop.first %}if{% else %}else if{% endif %} #[cfg(feature = "{{ board }}")] {