Add comprehensive guides for new module, sensor, and hardware variant development

.github/prompts/new-module.prompt.md

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+# New Meshtastic Module
+
+Guide for developing a new Meshtastic firmware module.
+
+## Module Hierarchy
+
+Choose the appropriate base class:
+
+1. **`MeshModule`** — Raw base class. Override `wantPacket()` and `handleReceived()`. Returns `ProcessMessage::STOP` or `ProcessMessage::CONTINUE`.
+2. **`SinglePortModule`** — Handles a single `meshtastic_PortNum`. Constructor takes `(name, portNum)`. Simplified `wantPacket()` checking `decoded.portnum`. Use `allocDataPacket()` to create outgoing packets.
+3. **`ProtobufModule<T>`** — Template for protobuf-encoded modules. Constructor takes `(name, portNum, fields)`. Override `handleReceivedProtobuf()`. Use `allocDataProtobuf(payload)` to create outgoing packets.
+
+Most modules also mix in `concurrency::OSThread` for periodic background tasks.
+
+## Implementation Pattern
+
+```cpp
+// src/modules/MyModule.h
+#pragma once
+#include "ProtobufModule.h"
+#include "concurrency/OSThread.h"
+
+class MyModule : public ProtobufModule<meshtastic_MyMessage>, private concurrency::OSThread
+{
+  public:
+    MyModule();
+
+  protected:
+    // Process incoming protobuf packet. Return true to stop further processing.
+    virtual bool handleReceivedProtobuf(const meshtastic_MeshPacket &mp, meshtastic_MyMessage *msg) override;
+
+    // Generate response packet (optional)
+    virtual meshtastic_MeshPacket *allocReply() override;
+
+    // Periodic task — return next run interval in ms, or disable()
+    virtual int32_t runOnce() override;
+
+    // Modify packet in-flight before delivery (optional)
+    virtual bool alterReceivedProtobuf(meshtastic_MeshPacket &mp, meshtastic_MyMessage *msg);
+
+    // Request a UI display frame (optional)
+    virtual bool wantUIFrame();
+};
+```
+
+## Registration
+
+Register in `src/modules/Modules.cpp` inside `setupModules()`:
+
+```cpp
+#if !MESHTASTIC_EXCLUDE_MYMODULE
+    new MyModule();
+#endif
+```
+
+If other code needs to reference the module instance:
+
+```cpp
+#if !MESHTASTIC_EXCLUDE_MYMODULE
+    myModule = new MyModule();
+#endif
+```
+
+And declare the global in the header:
+
+```cpp
+extern MyModule *myModule;
+```
+
+Some modules also conditionally instantiate based on `moduleConfig`:
+
+```cpp
+#if !MESHTASTIC_EXCLUDE_MYMODULE
+    if (moduleConfig.has_my_module && moduleConfig.my_module.enabled) {
+        new MyModule();
+    }
+#endif
+```
+
+## Conditional Compilation
+
+Add a `MESHTASTIC_EXCLUDE_MYMODULE` guard. This allows the module to be excluded from constrained builds. The flag name must follow the pattern: `MESHTASTIC_EXCLUDE_` + uppercase module name.
+
+## Protobuf Messages (if needed)
+
+1. Define messages in `protobufs/meshtastic/` (e.g., `mymodule.proto`)
+2. Add a `.options` file for nanopb field size constraints
+3. Regenerate with `bin/regen-protos.sh`
+4. Generated code appears in `src/mesh/generated/meshtastic/`
+5. Assign a `meshtastic_PortNum` if the module uses a new port number
+
+## Timing and Defaults
+
+Use `Default` class helpers for configurable intervals:
+
+```cpp
+int32_t MyModule::runOnce()
+{
+    uint32_t interval = Default::getConfiguredOrDefaultMs(moduleConfig.my_module.update_interval,
+                                                          default_my_module_interval);
+    // ... do work ...
+    return interval;
+}
+```
+
+On public/default channels, enforce minimums with `Default::getConfiguredOrMinimumValue()`.
+
+## Observer Pattern
+
+Subscribe to system events:
+
+```cpp
+CallbackObserver<MyModule, const meshtastic::Status *> statusObserver =
+    CallbackObserver<MyModule, const meshtastic::Status *>(this, &MyModule::handleStatusUpdate);
+```
+
+## Testing
+
+Add test suite in `test/test_mymodule/`:
+
+```
+test/
+└── test_mymodule/
+    └── test_main.cpp
+```
+
+Run with: `pio test -e native`
+
+## Checklist
+
+- [ ] Header and implementation files in `src/modules/`
+- [ ] Inherit from appropriate base class (MeshModule / SinglePortModule / ProtobufModule)
+- [ ] Mix in OSThread if periodic work is needed
+- [ ] Register in `src/modules/Modules.cpp` with `MESHTASTIC_EXCLUDE_` guard
+- [ ] Add protobuf definitions if needed (`protobufs/meshtastic/`)
+- [ ] Use `Default::getConfiguredOrDefaultMs()` for timing
+- [ ] Respect bandwidth limits on public channels
+- [ ] Add test suite in `test/`