chore: create .custom and .icons in overrides

Changes:
1. Extract `.icons/icon-mono.svg` from `~picodata-link.html`
2. Rename: partials/~picodata-link.html -> .custom/source-picodata.html
3. Rename: partials/~icon.html -> .custom/icon.html
4. Sync `source-picodata.html` with the template `source.html`
5. Edit `header.html` and `nav.html`

See:
https://github.com/squidfunk/mkdocs-material/blob/master/src/templates/partials/source.html

overrides/.custom/source-picodata.html

+<!--
+  Copyright (c) 2016-2024 Martin Donath <martin.donath@squidfunk.com>
+
+  Permission is hereby granted, free of charge, to any person obtaining a copy
+  of this software and associated documentation files (the "Software"), to
+  deal in the Software without restriction, including without limitation the
+  rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+  sell copies of the Software, and to permit persons to whom the Software is
+  furnished to do so, subject to the following conditions:
+
+  The above copyright notice and this permission notice shall be included in
+  all copies or substantial portions of the Software.
+
+  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+  FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL THE
+  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+  FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+  IN THE SOFTWARE.
+-->
+
+<!-- Site information -->
+<a
+  href="https://picodata.io/"
+  title="Сайт Picodata"
+  class="md-source"
+  data-md-component="source"
+  target="_blank"
+  rel="noopener"
+>
+  <div class="md-source__icon md-icon">
+    {% include ".icons/icon-mono.svg" %}
+  </div>
+  <div class="md-source__repository">
+    Picodata
+  </div>
+</a>

overrides/partials/header.html

@@ -53,7 +53,7 @@
     </label>
 
     <!-- Header title -->
-    {% include "partials/~icon.html" %}
+    {% include ".custom/icon.html" %}
     <div class="md-header__title" data-md-component="header-title">
       <div class="md-header__ellipsis">
         <div class="md-header__topic">
@@ -167,7 +167,7 @@
 
     <!-- Link to Picodata site -->
     <div class="md-header__source picodata-link">
-      {% include "partials/~picodata-link.html" %}
+      {% include ".custom/source-picodata.html" %}
     </div>
   </nav>
 

overrides/partials/nav.html

@@ -61,7 +61,7 @@
 
   <!-- Link to Picodata site -->
   <div class="md-nav__source">
-    {% include "partials/~picodata-link.html" %}
+    {% include ".custom/source-picodata.html" %}
   </div>
 
   <!-- Navigation list -->