docs(phpdoc): document public methods across src/

Add professional PHPDoc (summary + @param/@return) to the remaining
public methods that had none or only partial coverage: GraphController's
actions, ContributionStore's accessors, SvgRenderer's render() and
private helpers (with concrete array-shape annotations), ProbeTrait,
ProviderHealthChecker, ProviderStatus, and the Contribution entity.
Also adds the matching @return shapes on SvgRendererTest's data
providers.

src/Service/Renderer/SvgRenderer.php

@@ -36,6 +36,12 @@ final class SvgRenderer
     private const MARGIN_Y  = 20;   // top margin for month labels
     private const PADDING   = 10;   // outer padding
 
+    /**
+     * Builds the full self-contained SVG heatmap for a contribution map.
+     *
+     * @param array<string, int> $contributions date (Y-m-d) => contribution count
+     * @param string             $theme         "dark" or "light"; unknown values fall back to "dark"
+     */
     public function render(array $contributions, string $theme = 'dark'): string
     {
         $colors = self::THEMES[$theme] ?? self::THEMES['dark'];
@@ -91,6 +97,9 @@ final class SvgRenderer
     /**
      * Builds a [week][day] grid where each cell is ['date' => 'Y-m-d', 'count' => int]
      * or null if the date is in the future.
+     *
+     * @param  array<string, int> $contributions date (Y-m-d) => contribution count
+     * @return array<int, array<int, array{date: string, count: int}|null>>
      */
     private function buildGrid(\DateTimeImmutable $start, \DateTimeImmutable $today, array $contributions): array
     {
@@ -125,6 +134,10 @@ final class SvgRenderer
         };
     }
 
+    /**
+     * @param  array<string, int> $contributions date (Y-m-d) => contribution count
+     * @return array{total: int}
+     */
     private function computeStats(array $contributions): array
     {
         return ['total' => array_sum($contributions)];
@@ -132,6 +145,7 @@ final class SvgRenderer
 
     // -------------------------------------------------------------------------
 
+    /** @param array<int, array<int, array{date: string, count: int}|null>> $grid */
     private function renderMonthLabels(array $grid, string $textColor): string
     {
         $out       = '';
@@ -183,6 +197,10 @@ final class SvgRenderer
         return $out;
     }
 
+    /**
+     * @param array<int, array<int, array{date: string, count: int}|null>> $grid
+     * @param array{bg: string, text: string, levels: array<int, string>}  $colors
+     */
     private function renderCells(array $grid, array $colors): string
     {
         $out = '';
@@ -218,6 +236,7 @@ final class SvgRenderer
         return $out;
     }
 
+    /** @param array{bg: string, text: string, levels: array<int, string>} $colors */
     private function renderLegend(int $totalH, array $colors): string
     {
         $y   = $totalH - 14;