chore(clean): dedup card CSS via grouped selectors (CLN-3)

Shared chrome/hover/head/title/tag blocks for stack/project/theme cards +
methode items; per-class blocks keep only specifics. Zero HTML change,
cascade-order verified (no interfering rules between shared and specific
blocks). Net -60 lines; the audit's ~421 estimate was overstated.

index.html

@@ -419,39 +419,49 @@
     gap: 20px;
     margin-top: 40px;
   }
-  .stack-card {
+  /* ── Shared card chrome (stack / project / theme cards + méthode items).
+     Per-class blocks below keep only their specifics; the cascade resolves
+     identically to the previous duplicated declarations. ── */
+  .stack-card, .project-card, .theme-card, .methode-item {
     background: var(--page);
     border: 1px solid var(--rule);
     border-radius: var(--r-md);
-    padding: 24px;
     transition: border-color .25s ease, transform .25s ease, box-shadow .25s ease;
   }
-  .stack-card:hover {
+  .stack-card:hover, .project-card:hover, .theme-card:hover, .methode-item:hover {
     border-color: var(--g300);
     transform: translateY(-2px);
     box-shadow: var(--shadow-md);
   }
-  .stack-card-head {
+  .stack-card-head, .project-card-head, .theme-card-head {
     display: flex;
     align-items: baseline;
     justify-content: space-between;
-    margin-bottom: 16px;
-    padding-bottom: 12px;
     border-bottom: 1px dashed var(--rule);
   }
-  .stack-card h3 {
+  .stack-card h3, .project-card h3, .theme-card h4, .methode-body h3 {
     font-family: var(--serif);
     font-weight: 600;
-    font-size: 19px;
     color: var(--ink-1);
     letter-spacing: -0.01em;
   }
-  .stack-card-tag {
+  .stack-card-tag, .project-card-tag, .theme-card-tag {
     font-family: var(--mono);
     font-size: 11px;
     color: var(--g500);
     letter-spacing: 0.1em;
   }
+
+  .stack-card {
+    padding: 24px;
+  }
+  .stack-card-head {
+    margin-bottom: 16px;
+    padding-bottom: 12px;
+  }
+  .stack-card h3 {
+    font-size: 19px;
+  }
   .pills {
     display: flex;
     flex-wrap: wrap;
@@ -641,40 +651,19 @@
   }
   @media (min-width: 768px) { .projects-grid { grid-template-columns: repeat(2, 1fr); } }
   .project-card {
-    background: var(--page);
-    border: 1px solid var(--rule);
-    border-radius: var(--r-md);
     padding: 24px;
-    transition: border-color .25s ease, transform .25s ease, box-shadow .25s ease;
     display: flex;
     flex-direction: column;
   }
-  .project-card:hover {
-    border-color: var(--g300);
-    transform: translateY(-2px);
-    box-shadow: var(--shadow-md);
-  }
   .project-card-head {
-    display: flex;
-    align-items: baseline;
-    justify-content: space-between;
     gap: 12px;
     margin-bottom: 12px;
     padding-bottom: 10px;
-    border-bottom: 1px dashed var(--rule);
   }
   .project-card h3 {
-    font-family: var(--serif);
-    font-weight: 600;
     font-size: 20px;
-    color: var(--ink-1);
-    letter-spacing: -0.01em;
   }
   .project-card-tag {
-    font-family: var(--mono);
-    font-size: 11px;
-    color: var(--g500);
-    letter-spacing: 0.1em;
     flex-shrink: 0;
     white-space: nowrap;
   }
@@ -732,41 +721,20 @@
   @media (min-width: 1200px) { .formation-themes { grid-template-columns: repeat(3, 1fr); } }
 
   .theme-card {
-    background: var(--page);
-    border: 1px solid var(--rule);
-    border-radius: var(--r-md);
     padding: 22px;
-    transition: border-color .25s ease, transform .25s ease, box-shadow .25s ease;
     display: flex;
     flex-direction: column;
   }
-  .theme-card:hover {
-    border-color: var(--g300);
-    transform: translateY(-2px);
-    box-shadow: var(--shadow-md);
-  }
   .theme-card-head {
-    display: flex;
-    align-items: baseline;
-    justify-content: space-between;
     gap: 12px;
     margin-bottom: 12px;
     padding-bottom: 10px;
-    border-bottom: 1px dashed var(--rule);
   }
   .theme-card h4 {
-    font-family: var(--serif);
-    font-weight: 600;
     font-size: 18px;
-    color: var(--ink-1);
-    letter-spacing: -0.01em;
     line-height: 1.2;
   }
   .theme-card-tag {
-    font-family: var(--mono);
-    font-size: 11px;
-    color: var(--g500);
-    letter-spacing: 0.1em;
     flex-shrink: 0;
   }
   .theme-quote {
@@ -861,16 +829,7 @@
     grid-template-columns: 56px 1fr;
     gap: 20px;
     align-items: start;
-    background: var(--page);
-    border: 1px solid var(--rule);
-    border-radius: var(--r-md);
     padding: 22px 24px;
-    transition: border-color .25s ease, transform .25s ease, box-shadow .25s ease;
-  }
-  .methode-item:hover {
-    border-color: var(--g300);
-    transform: translateY(-2px);
-    box-shadow: var(--shadow-md);
   }
   .methode-num {
     font-family: var(--mono);
@@ -882,11 +841,7 @@
     padding-top: 4px;
   }
   .methode-body h3 {
-    font-family: var(--serif);
-    font-weight: 600;
     font-size: 19px;
-    color: var(--ink-1);
-    letter-spacing: -0.01em;
     margin-bottom: 6px;
     line-height: 1.25;
   }