feat(hikes): in-season toggle + unified canton/country filter

Add two filters to the /hikes filter panel:

- "Nur Touren in der aktuellen Saison" toggle — keeps only hikes whose
  recommended season window covers the current month (year-wrap aware;
  hikes without a window count as year-round).
- "Kanton / Land" — a typeahead that abstracts the hike's area over the
  border: Swiss hikes group by canton (coat-of-arms), hikes abroad by
  country (flag). Generalised the tag typeahead into ChipTypeahead
  (optional icon + label mapping) and reused it for both tags and areas.

Supporting bits: countries.ts (ISO/name → flag), hikeArea.ts (the
canton-or-country resolver, namespaced so codes can't collide), prepared
flag SVGs for CH/DE/IT/AT/FR, and an optional `country` field on the hike
manifest type (populated by the build script; the app falls back to canton
for Swiss hikes until a rebuild).

static/countries/at.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 3 2"><rect width="3" height="2" fill="#ed2939"/><rect width="3" height="0.6667" y="0.6667" fill="#fff"/></svg>

static/countries/ch.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32"><rect width="32" height="32" fill="#d52b1e"/><rect x="13" y="6" width="6" height="20" fill="#fff"/><rect x="6" y="13" width="20" height="6" fill="#fff"/></svg>

static/countries/de.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 5 3"><rect width="5" height="3" fill="#ffce00"/><rect width="5" height="2" fill="#d00"/><rect width="5" height="1" fill="#000"/></svg>

static/countries/fr.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 3 2"><rect width="3" height="2" fill="#ef4135"/><rect width="2" height="2" fill="#fff"/><rect width="1" height="2" fill="#0055a4"/></svg>

static/countries/it.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 3 2"><rect width="3" height="2" fill="#ce2b37"/><rect width="2" height="2" fill="#fff"/><rect width="1" height="2" fill="#009246"/></svg>