Fix zones loading and mock data system

Critical fixes:
- Zones now load correctly: fixed snapcast mock to emit { result: buildStatus() }
- Mock data now enabled by default: VITE_USE_MOCK=true in docker-compose.dev.yml
- Added initial status broadcast and periodic updates (5s) in snapcast mock

NMEA2000 data enhancements:
- Added realistic fuel rate monitoring (10-15 L/hr)
- Added alternator output (30-60A)
- Added engine hours counter (continuous)
- Added tank level monitoring (fresh water, waste water, bilge)
- Added depth alarm threshold
- All values use correct SI units (radians, m/s, Kelvin)
- Data changes smoothly with random walk algorithm (no jumps)
- Position advances based on heading and speed

Documentation:
- Added MOCK_DATA_EXPLANATION.md with complete guide
- Explains NMEA 2000 standard
- Documents all 3 mock data sources
- Includes troubleshooting and customization guide

Changes:
- dashboard/src/mock/snapcast.mock.js: Fixed event format and added periodic updates
- dashboard/src/mock/signalk.mock.js: Enhanced with 7 new realistic parameters
- docker-compose.dev.yml: Set VITE_USE_MOCK=true for dev mode
- MOCK_DATA_EXPLANATION.md: New comprehensive documentation

Now zones load on app startup and all mock data is realistic and working!

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

dashboard/src/mock/signalk.mock.js

@@ -36,6 +36,13 @@ export function createSignalKMock() {
     rudder: 2.5,
     airTemp: 14.2,
     fuel: 68,
+    fuelRate: 12.5,     // liters/hour
+    engineHours: 2847,
+    alternatorOutput: 45,  // amps
+    depthAlarm: 4.5,       // meters
+    waterUsed: 23,         // liters
+    wasteWater: 18,        // liters
+    freshWater: 156,       // liters
   }
 
   // Simulate boat moving along a rough course
@@ -60,6 +67,12 @@ export function createSignalKMock() {
     state.battery2  = randomWalk(state.battery2, 24.5, 25.6, 0.04)
     state.waterTemp = randomWalk(state.waterTemp, 16, 20, 0.05)
     state.rudder    = randomWalk(state.rudder, -15, 15, 1.5)
+    state.fuelRate  = randomWalk(state.fuelRate, 10, 15, 0.2)
+    state.alternatorOutput = randomWalk(state.alternatorOutput, 30, 60, 2)
+    state.waterUsed = randomWalk(state.waterUsed, 10, 30, 0.05)
+    state.wasteWater = randomWalk(state.wasteWater, 5, 25, 0.04)
+    state.freshWater = randomWalk(state.freshWater, 80, 160, 0.02)
+    state.engineHours += 0.016  // 1 hour per 60 seconds
     advancePosition()
 
     return {
@@ -67,20 +80,43 @@ export function createSignalKMock() {
         source: { label: 'mock', type: 'NMEA2000' },
         timestamp: new Date().toISOString(),
         values: [
+          // Navigation
           { path: 'navigation.speedOverGround',       value: state.sog * 0.514 },
           { path: 'navigation.courseOverGroundTrue',  value: degToRad(state.cog) },
           { path: 'navigation.headingTrue',           value: degToRad(state.heading) },
           { path: 'navigation.position',              value: { latitude: state.lat, longitude: state.lon } },
+          
+          // Depth & water
           { path: 'environment.depth.belowKeel',      value: state.depth },
+          { path: 'environment.water.temperature',    value: state.waterTemp + 273.15 },
+          
+          // Wind
           { path: 'environment.wind.speedApparent',   value: state.windSpeed * 0.514 },
           { path: 'environment.wind.angleApparent',   value: degToRad(state.windAngle) },
-          { path: 'environment.water.temperature',    value: state.waterTemp + 273.15 },
+          
+          // Air
           { path: 'environment.outside.temperature',  value: state.airTemp + 273.15 },
+          
+          // Engine
           { path: 'propulsion.main.revolutions',      value: state.rpm / 60 },
+          { path: 'propulsion.main.fuelRate',         value: state.fuelRate / 3600 },  // kg/s (approximated)
+          { path: 'propulsion.main.alternatorOutput', value: state.alternatorOutput },
+          
+          // Electrical
           { path: 'electrical.batteries.starter.voltage', value: state.battery1 },
           { path: 'electrical.batteries.house.voltage',   value: state.battery2 },
+          
+          // Steering
           { path: 'steering.rudderAngle',             value: degToRad(state.rudder) },
+          
+          // Tanks (as ratio 0-1)
           { path: 'tanks.fuel.0.currentLevel',        value: state.fuel / 100 },
+          { path: 'tanks.freshWater.0.currentLevel',  value: state.freshWater / 200 },
+          { path: 'tanks.wasteWater.0.currentLevel',  value: state.wasteWater / 50 },
+          { path: 'tanks.wasteWater.0.pumpOverride',  value: state.wasteWater > 30 },
+          
+          // Engine hours (seconds)
+          { path: 'propulsion.main.engineHours',      value: state.engineHours * 3600 },
         ]
       }]
     }