Swap flag emoji for real (square, bordered) SVG flags

Emoji flags are font glyphs, not shapes — no way to resize, border, or
tone them down to fit this app's controlled, hand-drawn-icon look
(same reasoning the topbar readout already settled earlier this
session). Vendored flag-icons' pre-cropped square SVGs (MIT) instead,
framed in a small rounded-square badge — the same convention
icons.js's MAP_MARKER_ICON already uses for framing a glyph, not a new
visual language.

public/vendor/flag-icons/1x1/gr.svg

@@ -0,0 +1,16 @@
+<svg xmlns="http://www.w3.org/2000/svg" id="flag-icons-gr" viewBox="0 0 512 512">
+  <path fill="#0d5eaf" fill-rule="evenodd" d="M0 0h512v57H0z"/>
+  <path fill="#fff" fill-rule="evenodd" d="M0 57h512v57H0z"/>
+  <path fill="#0d5eaf" fill-rule="evenodd" d="M0 114h512v57H0z"/>
+  <path fill="#fff" fill-rule="evenodd" d="M0 171h512v57H0z"/>
+  <path fill="#0d5eaf" fill-rule="evenodd" d="M0 228h512v56.9H0z"/>
+  <path fill="#fff" fill-rule="evenodd" d="M0 284.9h512v57H0z"/>
+  <path fill="#0d5eaf" fill-rule="evenodd" d="M0 341.9h512v57H0z"/>
+  <path fill="#fff" fill-rule="evenodd" d="M0 398.9h512v57H0z"/>
+  <path fill="#0d5eaf" d="M0 0h284.9v284.9H0z"/>
+  <g fill="#fff" fill-rule="evenodd" stroke-width="1.3">
+    <path d="M114 0h57v284.9h-57z"/>
+    <path d="M0 114h284.9v57H0z"/>
+  </g>
+  <path fill="#0d5eaf" fill-rule="evenodd" d="M0 455h512v57H0z"/>
+</svg>