Update to sinatra 4, update puma, add 404 handler

Gemfile

@@ -1,6 +1,6 @@
 source 'https://rubygems.org'
 
-gem 'sinatra'
+gem 'sinatra', '~> 4.0'
 gem 'sqlite3'
 gem 'json'
 gem 'puma'

Gemfile.lock

@@ -1,32 +1,40 @@
 GEM
   remote: https://rubygems.org/
   specs:
-    json (2.6.3)
-    mustermann (2.0.2)
+    base64 (0.2.0)
+    json (2.7.1)
+    mustermann (3.0.0)
       ruby2_keywords (~> 0.0.1)
-    nio4r (2.5.9)
-    puma (6.4.0)
+    nio4r (2.7.0)
+    puma (6.4.2)
       nio4r (~> 2.0)
-    rack (2.2.8)
-    rack-protection (2.2.4)
-      rack
+    rack (3.0.8)
+    rack-protection (4.0.0)
+      base64 (>= 0.1.0)
+      rack (>= 3.0.0, < 4)
+    rack-session (2.0.0)
+      rack (>= 3.0.0)
     ruby2_keywords (0.0.5)
-    sinatra (2.2.4)
-      mustermann (~> 2.0)
-      rack (~> 2.2)
-      rack-protection (= 2.2.4)
+    sinatra (4.0.0)
+      mustermann (~> 3.0)
+      rack (>= 3.0.0, < 4)
+      rack-protection (= 4.0.0)
+      rack-session (>= 2.0.0, < 3)
       tilt (~> 2.0)
-    sqlite3 (1.6.1-arm64-darwin)
-    tilt (2.0.11)
+    sqlite3 (1.7.0-arm64-darwin)
+    sqlite3 (1.7.0-x86_64-linux)
+    tilt (2.3.0)
 
 PLATFORMS
   arm64-darwin-22
+  arm64-darwin-23
+  x86_64-linux
 
 DEPENDENCIES
   json
   puma
-  sinatra
+  sinatra (~> 4.0)
   sqlite3
 
 BUNDLED WITH
-   2.4.12
+   2.5.5

csp_reporter.rb

@@ -47,3 +47,7 @@ def authorized?
   @reports = DB.execute("SELECT * FROM CSP_Reports ORDER BY created_at DESC LIMIT 1000")
   erb :reports
 end
+
+not_found do
+  'Not found ¯\_(ツ)_/¯'
+end