Add tianwen-gui: N.I.N.A.-style integrated GUI with Planner tab

New TianWen.UI.Gui project using SDL3+Vulkan with left sidebar navigation:
- Left sidebar (P/V/S/E) with active tab highlighting and hover states
- Top status bar with profile name, night window times, and clock
- Planner tab: altitude chart (AltitudeChartRenderer), scrollable target
  list with proposed/selected highlighting, details panel
- Keyboard: ↑↓ navigate, Enter toggle proposal, P priority, S schedule
- Mouse: sidebar tab switching, target list click selection, scroll wheel

Also extracts TransformFactory from CLI's LocationResolver into Abstractions
so both CLI and GUI can create Transform from profile mount URI.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: sebgod

src/TianWen.Lib.CLI/Plan/LocationResolver.cs

@@ -1,54 +1,24 @@
-using System.Globalization;
-using System.Web;
 using TianWen.Lib.Astrometry.SOFA;
 using TianWen.Lib.Devices;
+using TianWen.UI.Abstractions;
 
 namespace TianWen.Lib.CLI.Plan;
 
 /// <summary>
-/// Resolves site latitude/longitude/elevation from the active profile's mount URI.
+/// CLI wrapper around <see cref="TransformFactory"/> that reports errors via <see cref="IConsoleHost"/>.
 /// </summary>
 internal static class LocationResolver
 {
-    /// <summary>
-    /// Creates a <see cref="Transform"/> configured with the site location from the profile's mount URI.
-    /// </summary>
     public static Transform? ResolveFromProfile(
         IConsoleHost consoleHost,
         Profile profile,
         TimeProvider timeProvider)
     {
-        var data = profile.Data;
-        if (data is null || data.Value.Mount == NoneDevice.Instance.DeviceUri)
+        var transform = TransformFactory.FromProfile(profile, timeProvider, out var error);
+        if (error is not null)
         {
-            consoleHost.WriteError("Profile has no mount configured. Use 'tianwen profile set-mount' first.");
-            return null;
+            consoleHost.WriteError(error);
         }
-
-        var query = HttpUtility.ParseQueryString(data.Value.Mount.Query);
-        var latStr = query[DeviceQueryKey.Latitude.Key];
-        var lonStr = query[DeviceQueryKey.Longitude.Key];
-        var elevStr = query[DeviceQueryKey.Elevation.Key];
-
-        if (latStr is null || lonStr is null ||
-            !double.TryParse(latStr, CultureInfo.InvariantCulture, out var lat) ||
-            !double.TryParse(lonStr, CultureInfo.InvariantCulture, out var lon))
-        {
-            consoleHost.WriteError("Mount URI does not contain latitude/longitude. Use 'tianwen profile set-site' to configure.");
-            return null;
-        }
-
-        var elevation = elevStr is not null && double.TryParse(elevStr, CultureInfo.InvariantCulture, out var elev)
-            ? elev
-            : 0.0;
-
-        return new Transform(timeProvider)
-        {
-            SiteLatitude = lat,
-            SiteLongitude = lon,
-            SiteElevation = elevation,
-            SiteTemperature = 15,
-            DateTimeOffset = timeProvider.GetLocalNow()
-        };
+        return transform;
     }
 }

src/TianWen.UI.Abstractions/TransformFactory.cs

@@ -0,0 +1,55 @@
+using System;
+using System.Globalization;
+using System.Web;
+using TianWen.Lib.Astrometry.SOFA;
+using TianWen.Lib.Devices;
+
+namespace TianWen.UI.Abstractions;
+
+/// <summary>
+/// Creates a <see cref="Transform"/> from a profile's mount URI (latitude, longitude, elevation).
+/// Shared between CLI and GUI.
+/// </summary>
+public static class TransformFactory
+{
+    /// <summary>
+    /// Creates a Transform from the profile's mount URI query params.
+    /// Returns null with an error message if the profile has no mount or no lat/lon.
+    /// </summary>
+    public static Transform? FromProfile(Profile profile, TimeProvider timeProvider, out string? error)
+    {
+        error = null;
+        var data = profile.Data;
+        if (data is null || data.Value.Mount == NoneDevice.Instance.DeviceUri)
+        {
+            error = "Profile has no mount configured. Use 'tianwen profile set-mount' first.";
+            return null;
+        }
+
+        var query = HttpUtility.ParseQueryString(data.Value.Mount.Query);
+        var latStr = query[DeviceQueryKey.Latitude.Key];
+        var lonStr = query[DeviceQueryKey.Longitude.Key];
+        var elevStr = query[DeviceQueryKey.Elevation.Key];
+
+        if (latStr is null || lonStr is null ||
+            !double.TryParse(latStr, CultureInfo.InvariantCulture, out var lat) ||
+            !double.TryParse(lonStr, CultureInfo.InvariantCulture, out var lon))
+        {
+            error = "Mount URI does not contain latitude/longitude. Use 'tianwen profile set-site' to configure.";
+            return null;
+        }
+
+        var elevation = elevStr is not null && double.TryParse(elevStr, CultureInfo.InvariantCulture, out var elev)
+            ? elev
+            : 0.0;
+
+        return new Transform(timeProvider)
+        {
+            SiteLatitude = lat,
+            SiteLongitude = lon,
+            SiteElevation = elevation,
+            SiteTemperature = 15,
+            DateTimeOffset = timeProvider.GetLocalNow()
+        };
+    }
+}

src/TianWen.UI.Gui/GuiAppState.cs

@@ -0,0 +1,20 @@
+using TianWen.Lib.Devices;
+
+namespace TianWen.UI.Gui;
+
+public enum GuiTab
+{
+    Planner,
+    Viewer,
+    Session,
+    Equipment
+}
+
+public class GuiAppState
+{
+    public GuiTab ActiveTab { get; set; } = GuiTab.Planner;
+    public Profile? ActiveProfile { get; set; }
+    public bool NeedsRedraw { get; set; } = true;
+    public (float X, float Y) MouseScreenPosition { get; set; }
+    public string? StatusMessage { get; set; }
+}