feat: Add comprehensive address-first geolocation system for events

This implementation provides automatic geocoding and map integration:

- **Event Model Enhancements:**
  - Automatic geocoding callback using OpenStreetMap Nominatim API
  - 3-tier fallback system: exact coordinates → city-based → country default
  - Fallback coordinates for major French cities (Paris, Lyon, Marseille, etc.)
  - Robust error handling that prevents event creation failures

- **User-Friendly Event Forms:**
  - Address-first approach - users just enter addresses
  - Hidden coordinate fields (auto-generated behind scenes)
  - Real-time geocoding with 1.5s debounce
  - "Ma position" button for current location with reverse geocoding
  - "Prévisualiser" button to show map links
  - Smart feedback system (loading, success, warnings, errors)

- **Enhanced Event Show Page:**
  - Map provider links (OpenStreetMap, Google Maps, Apple Plans)
  - Warning badges when approximate coordinates are used
  - Address-based URLs for better map integration

- **Comprehensive JavaScript Controller:**
  - Debounced auto-geocoding to minimize API calls
  - Multiple geocoding strategies (manual vs automatic)
  - Promise-based geolocation with proper error handling
  - Dynamic map link generation with address + coordinates

- **Failure Handling:**
  - Events never fail to save due to missing coordinates
  - Fallback to city-based coordinates when exact geocoding fails
  - User-friendly warnings when approximate locations are used
  - Maintains existing coordinates on update failures

🤖 Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

app/views/events/show.html.erb

@@ -1,5 +1,5 @@
 <div class="min-h-screen bg-gradient-to-br from-gray-50 to-gray-100">
-  <div class="max-w-7xl mx-auto px-4 sm:px-6 lg:px-8 py-8">
+  <div class="max-w-6xl mx-auto px-4 sm:px-6 lg:px-8 py-8">
     <!-- Breadcrumb -->
     <%= render 'components/breadcrumb', crumbs: [
       { name: 'Accueil', path: root_path },
@@ -55,7 +55,48 @@
                   Lieu
                 </h3>
                 <p class="text-gray-700 font-medium"><%= @event.venue_name %></p>
-                <p class="text-gray-600 mt-1"><%= @event.venue_address %></p>
+                <p class="text-gray-600 mt-2 mb-4"><%= @event.venue_address %></p>
+                
+                <% if @event.latitude.present? && @event.longitude.present? %>
+                  <div class="border-t border-gray-200 pt-4">
+                    <% if @event.geocoding_status_message %>
+                      <div class="mb-3 p-2 bg-yellow-50 border border-yellow-200 rounded-lg">
+                        <div class="flex items-center">
+                          <i data-lucide="alert-triangle" class="w-4 h-4 text-yellow-600 mr-2"></i>
+                          <p class="text-xs text-yellow-800"><%= @event.geocoding_status_message %></p>
+                        </div>
+                      </div>
+                    <% end %>
+                    <p class="text-sm font-medium text-gray-700 mb-2">Ouvrir dans :</p>
+                    <div class="flex flex-wrap gap-2">
+                      <% 
+                        encoded_address = URI.encode_www_form_component(@event.venue_address)
+                        lat = @event.latitude
+                        lng = @event.longitude
+                        
+                        map_providers = {
+                          "OpenStreetMap" => "https://www.openstreetmap.org/?mlat=#{lat}&mlon=#{lng}#map=16/#{lat}/#{lng}",
+                          "Google Maps" => "https://www.google.com/maps/search/#{encoded_address}/@#{lat},#{lng},16z",
+                          "Apple Plans" => "https://maps.apple.com/?address=#{encoded_address}&ll=#{lat},#{lng}"
+                        }
+                        
+                        icons = {
+                          "OpenStreetMap" => "🗺️",
+                          "Google Maps" => "🔍", 
+                          "Apple Plans" => "🍎"
+                        }
+                      %>
+                      
+                      <% map_providers.each do |name, url| %>
+                        <%= link_to url, target: "_blank", rel: "noopener", 
+                            class: "inline-flex items-center px-3 py-2 text-xs font-medium text-gray-700 bg-white border border-gray-300 rounded-lg hover:bg-gray-50 transition-colors" do %>
+                          <span class="mr-1"><%= icons[name] %></span>
+                          <%= name %>
+                        <% end %>
+                      <% end %>
+                    </div>
+                  </div>
+                <% end %>
               </div>
 
               <div class="bg-gray-50 rounded-xl p-6">
@@ -150,4 +191,4 @@
       </div>
     </div>
   </div>
-</div>
+</div>