fix: Replace Prawn with Grover for PDF ticket generation

- Replace Prawn PDF generation with Grover (Chrome headless) for better compatibility
- Add HTML-based ticket template with embedded CSS styling
- Implement robust Grover loading with fallback to HTML download
- Add QR code generation methods to Ticket model
- Remove legacy TicketPdfGenerator service and tests
- Update PDF generation in TicketsController with proper error handling

The new implementation provides:
- Better HTML/CSS rendering for ticket layouts
- More reliable PDF generation using Chrome engine
- Fallback mechanism for better user experience
- Cleaner separation of template rendering and PDF conversion

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

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

Gemfile.lock

@@ -127,6 +127,8 @@ GEM
       raabro (~> 1.4)
     globalid (1.2.1)
       activesupport (>= 6.1)
+    grover (1.2.3)
+      nokogiri (~> 1)
     i18n (1.14.7)
       concurrent-ruby (~> 1.0)
     io-console (0.8.1)
@@ -221,16 +223,8 @@ GEM
     parser (3.3.9.0)
       ast (~> 2.4.1)
       racc
-    pdf-core (0.10.0)
     pp (0.6.2)
       prettyprint
-    prawn (2.5.0)
-      matrix (~> 0.4)
-      pdf-core (~> 0.10.0)
-      ttfunk (~> 1.8)
-    prawn-qrcode (0.5.2)
-      prawn (>= 1)
-      rqrcode (>= 1.0.0)
     prettyprint (0.2.0)
     prism (1.4.0)
     propshaft (1.2.1)
@@ -378,8 +372,6 @@ GEM
     thruster (0.1.15-aarch64-linux)
     thruster (0.1.15-x86_64-linux)
     timeout (0.4.3)
-    ttfunk (1.8.0)
-      bigdecimal (~> 3.1)
     turbo-rails (2.0.16)
       actionpack (>= 7.1.0)
       railties (>= 7.1.0)
@@ -423,6 +415,7 @@ DEPENDENCIES
   debug
   devise (~> 4.9)
   dotenv-rails
+  grover
   jbuilder
   jsbundling-rails
   kamal
@@ -431,8 +424,6 @@ DEPENDENCIES
   minitest-reporters (~> 1.7)
   mocha
   mysql2 (~> 0.5)
-  prawn (~> 2.5)
-  prawn-qrcode (~> 0.5)
   propshaft
   puma (>= 5.0)
   rails (~> 8.0.2, >= 8.0.2.1)