feat(v0.1): historia cen + jawnosc cen — milestone Initial Release

Historia cen:
- Tabela wp_price_history z WP Cronem dziennym (snapshot cen)
- AJAX endpoint apartamenty_get_price_history (zabezpieczony nonce)
- Popup "Historia cen" w widgecie — vanilla JS, modal zgodny z projektem

Jawnosc cen:
- Endpointy /ceny-mieszkan.xml + /dane-gov-pl.xml (XSD-compliant)
- Pliki MD5 dla obu XML
- Strona admina: Narzedzia -> Jawnosc Cen z URL-ami do Ministerstwa
- Transient cache 1h z inwalidacja przez cron

Dokumentacja: docs/readme.md + docs/jawnosc-cen.md

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

wp-content/plugins/elementor-addon/assets/css/main.scss

@@ -275,3 +275,114 @@
 		}
 	}
 }
+
+// Historia cen — popup overlay
+.price-history-overlay {
+    display: none;
+    position: fixed;
+    inset: 0;
+    z-index: 99999;
+    background: rgba(25, 44, 68, 0.55);
+    align-items: center;
+    justify-content: center;
+    padding: 20px;
+
+    &.is-open {
+        display: flex;
+    }
+}
+
+.price-history-modal {
+    position: relative;
+    background: #fff;
+    border: 4px solid #192c44;
+    padding: 32px 36px 28px;
+    max-width: 560px;
+    width: 100%;
+    font-family: 'Barlow', sans-serif;
+    color: #192c44;
+
+    @media (max-width: 600px) {
+        padding: 24px 20px 20px;
+    }
+
+    &__close {
+        position: absolute;
+        top: 14px;
+        right: 14px;
+        background: none;
+        border: 2px solid #192c44;
+        width: 30px;
+        height: 30px;
+        display: flex;
+        align-items: center;
+        justify-content: center;
+        cursor: pointer;
+        padding: 0;
+        line-height: 1;
+    }
+
+    &__title {
+        font-size: 22px;
+        font-weight: 700;
+        margin: 0 0 18px;
+        padding-right: 40px;
+        color: #192c44;
+    }
+
+    &__current {
+        margin-bottom: 16px;
+    }
+
+    &__row {
+        display: flex;
+        justify-content: space-between;
+        font-size: 18px;
+        line-height: 1.5;
+        color: #192c44;
+
+        &--bold {
+            font-weight: 700;
+        }
+    }
+
+    &__val {
+        text-align: right;
+    }
+
+    &__table-wrap {
+        border-top: 1px solid #192c44;
+        padding-top: 12px;
+        margin-top: 4px;
+        max-height: 40vh;
+        overflow-y: auto;
+    }
+
+    &__table {
+        width: 100%;
+        border-collapse: collapse;
+
+        tr {
+            border: none;
+            background: transparent;
+
+            td {
+                padding: 4px 0;
+                font-size: 15px;
+                color: #192c44;
+                font-family: 'Barlow', sans-serif;
+                font-weight: 400;
+                border: none;
+                background: transparent;
+
+                &:last-child {
+                    text-align: right;
+                }
+
+                &:nth-child(2) {
+                    text-align: center;
+                }
+            }
+        }
+    }
+}