Add Four-Color algorithm page

Introduce an interactive Four Color Theorem demo: add FourColorComponent (template, styles, standalone component) with canvas-based grid, region generation, adjacency detection and a backtracking solver; include models for nodes/regions and grid constants. Wire up route and RouterConstants/UrlConstants, add menu entry in AlgorithmsService, and add i18n entries for English and German. Also add global color styles in styles.scss and a few minor i18n text adjustments.

src/assets/i18n/en.json

@@ -526,6 +526,10 @@
       "TITLE": "Maze Generation",
       "DESCRIPTION": "Visualizing various maze generation algorithms."
     },
+    "FOUR_COLOR": {
+      "TITLE": "Four Color Theorem",
+      "DESCRIPTION": "The four color theorem states that any map in a plane can be colored using at most four colors in such a way that regions sharing a common boundary (other than a single point) do not share the same color."
+    },
     "FRACTAL": {
       "TITLE": "Fractals",
       "DESCRIPTION": "Visualisation of complex geometric patterns that resemble each other on increasingly smaller scales (self-similarity)."
@@ -545,5 +549,35 @@
     "NOTE": "Note",
     "GRID_HEIGHT": "Height",
     "GRID_WIDTH": "Width"
+  },
+  "FOUR_COLOR": {
+    "TITLE": "Four Color Theorem",
+    "GENERATE": "Generate Map",
+    "SOLVE": "Auto Solve",
+    "CLEAR": "Clear Colors",
+    "COLOR_1": "Color 1",
+    "COLOR_2": "Color 2",
+    "COLOR_3": "Color 3",
+    "COLOR_4": "Color 4",
+    "EXECUTION_TIME": "Execution Time",
+    "STATUS": {
+      "LABEL": "Status",
+      "INCOMPLETE": "Map is not fully colored yet.",
+      "SOLVED": "Congratulations! You solved the map correctly!",
+      "CONFLICTS": "Warning: Adjacent regions have the same color!",
+      "INVALID": "Map is fully colored, but contains conflicts."
+    },
+    "EXPLANATION": {      "TITLE": "Four Color Theorem",
+      "EXPLANATION": "The four color theorem states that any map in a plane can be colored using at most four colors in such a way that regions sharing a common boundary (other than a single point) do not share the same color.",
+      "DISCLAIMER": "This algorithm uses backtracking to find a valid coloring for the generated regions.",
+      "DISCLAIMER_1": "Map Generation: Regions are generated using a random seed growth algorithm (Voronoi-like) on a grid.",
+      "DISCLAIMER_2": "Adjacency: Two regions are considered neighbors if they share at least one edge in the grid.",
+      "DISCLAIMER_3": "Backtracking: The solver tries colors 1-4 for each region, backtracking when a conflict is found.",
+      "DISCLAIMER_4": "Interactive: You can also click on regions to cycle through colors manually.",
+      "DISCLAIMER_BOTTOM": "Click to color the region. Click again to change the color."
+    },
+    "ALERT": {
+      "NO_SOLUTION": "No solution found (this should not happen for a planar map!)."
+    }
   }
 }