feat: Add localization template with grid-based sensor fusion

Implements comprehensive robot localization system as third template option.
Teams can now start with professional positioning and navigation code.

Template Features:
- 12x12 field grid system (12-inch cells)
- Multi-sensor fusion (encoders, IMU, vision)
- Kalman-filter-style sensor combination
- Fault-tolerant positioning (graceful degradation)
- 21 files, ~1,500 lines, 3 passing tests

Core Components:
- GridCell/Pose2D/FieldGrid - Coordinate system
- RobotLocalizer - Sensor fusion engine
- OdometryTracker - Dead reckoning from encoders
- ImuLocalizer - Heading from gyroscope
- VisionLocalizer - Position from AprilTags

Sensor Fusion Strategy:
Priority 1: Vision (AprilTags) → ±2" accuracy, 100% confidence
Priority 2: IMU + Odometry → ±4" accuracy, 70% confidence
Priority 3: Odometry only → ±12" accuracy, 40% confidence

System gracefully degrades when sensors fail, maintaining operation
even with partial sensor availability.

Hardware Abstraction:
- Interfaces (Encoder, GyroSensor, VisionCamera)
- Mock implementations for unit testing
- Teams implement FTC wrappers for their hardware

Documentation:
- LOCALIZATION_GUIDE.md - System architecture and usage
- GRID_SYSTEM.md - Field coordinate reference
- README.md - Quick start and examples

Usage:
  weevil new my-robot --template localization
  cd my-robot
  ./gradlew test  # 3 tests pass in < 1 second

This teaches professional robotics concepts (sensor fusion, fault
tolerance, coordinate systems) not found in other FTC tools. Positions
Nexus Workshops as teaching advanced autonomous programming.

Updated src/templates/mod.rs to register localization template with
proper metadata and feature descriptions.

All tests passing (10/10 template tests).

templates/localization/README.md.template

@@ -11,7 +11,7 @@ Grid-based robot localization with sensor fusion and fault tolerance.
 - **Grid System** - 12x12 field grid (12" cells)
 - **Sensor Fusion** - Combine encoders, IMU, vision
 - **Fault Tolerance** - Graceful sensor failure handling
-- **20+ Tests** - All passing
+- **3 Tests** - All passing
 
 ## Quick Start
 

templates/localization/docs/GRID_SYSTEM.md

@@ -11,7 +11,7 @@
  9  .   .   .   .   .   .   .   .   .   .   .   .
  8  .   .   .   .   .   .   .   .   .   .   .   .
  7  .   .   .   .   .   .   .   .   .   .   .   .
- 6  .   .   .   .   .   .   X   .   .   .   .   .
+ 6  .   .   .   .   .   X   .   .   .   .   .   .
  5  .   .   .   .   .   .   .   .   .   .   .   .
  4  .   .   .   .   .   .   .   .   .   .   .   .
  3  .   .   .   .   .   .   .   .   .   .   .   .

templates/localization/settings.gradle

@@ -1 +0,0 @@
-rootProject.name = '{{PROJECT_NAME}}'

templates/localization/settings.gradle.kts.template

@@ -0,0 +1,17 @@
+pluginManagement {
+    repositories {
+        google()
+        mavenCentral()
+        gradlePluginPortal()
+    }
+}
+
+dependencyResolutionManagement {
+    repositoriesMode.set(RepositoriesMode.PREFER_SETTINGS)
+    repositories {
+        mavenCentral()
+        google()
+    }
+}
+
+rootProject.name = "{{PROJECT_NAME}}"

templates/localization/src/main/java/robot/hardware/GyroSensor.java

@@ -4,4 +4,5 @@ public interface GyroSensor {
     double getHeading();
     boolean isConnected();
     void calibrate();
+    boolean isCalibrated();
 }

templates/localization/src/main/java/robot/localization/ImuLocalizer.java

@@ -13,14 +13,17 @@ public class ImuLocalizer {
     
     public void calibrate(double initialHeading) {
         if (gyro.isConnected()) {
+            gyro.calibrate();
             this.headingOffset = initialHeading - gyro.getHeading();
         }
     }
     
     public Double getHeading() {
-        if (!gyro.isConnected()) return null;
+        if (!gyro.isConnected() || !gyro.isCalibrated()) return null;
         return Pose2D.normalizeAngle(gyro.getHeading() + headingOffset);
     }
     
-    public boolean isWorking() { return gyro.isConnected(); }
+    public boolean isWorking() { 
+        return gyro.isConnected() && gyro.isCalibrated(); 
+    }
 }

templates/localization/src/test/java/robot/hardware/MockGyroSensor.java

@@ -3,11 +3,14 @@ package robot.hardware;
 public class MockGyroSensor implements GyroSensor {
     private double heading = 0;
     private boolean connected = true;
+    private boolean calibrated = true;
     
     public double getHeading() { return heading; }
     public boolean isConnected() { return connected; }
-    public void calibrate() { }
+    public void calibrate() { calibrated = true; }
+    public boolean isCalibrated() { return calibrated; }
     
     public void setHeading(double h) { heading = h; }
     public void setConnected(boolean c) { connected = c; }
+    public void setCalibrated(boolean c) { calibrated = c; }
 }

templates/localization/src/test/java/robot/localization/SensorFusionTest.java

@@ -34,11 +34,15 @@ class SensorFusionTest {
         MockGyroSensor gyro = new MockGyroSensor();
         MockVisionCamera camera = new MockVisionCamera();
         
+        // Set a pose so vision is actually "working" (not just connected)
+        camera.setPose(new Pose2D(12, 12, 0));
+        
         OdometryTracker odometry = new OdometryTracker(left, right);
         ImuLocalizer imu = new ImuLocalizer(gyro);
         VisionLocalizer vision = new VisionLocalizer(camera);
         
         RobotLocalizer localizer = new RobotLocalizer(odometry, imu, vision);
+        localizer.update();  // Need to update to actually use vision
         
         assertEquals(1.0, localizer.getConfidence(), 0.01);