Merge master and resolve conflicts

Resolved conflicts in favor of our more stable versions:
- Keep Ruby 3.4.6 (master had 3.4.3)
- Keep Shakapacker 9.3.3 stable (master had 9.3.4-beta.0)
- Keep Thruster HTTP/2 proxy integration (not in master)
- Keep Dockerfile improvements (FROM AS, SECRET_KEY_BASE handling)
- Keep early_hints debug: false (master doesn't have this config)

Accepted from master:
- GitHub Actions workflow updates for Ruby version
- react_on_rails 16.2.0.beta.10 (already had this)

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

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

Author: justin808

.github/workflows/js_test.yml

@@ -14,7 +14,7 @@ jobs:
       fail-fast: false
       matrix:
         node: [22.x]
-        ruby: [3.4.6]
+        ruby: [3.4.3]
 
     env:
       RAILS_ENV: test

.github/workflows/lint_test.yml

@@ -14,7 +14,7 @@ jobs:
       fail-fast: false
       matrix:
         node: [22.x]
-        ruby: [3.4.6]
+        ruby: [3.4.3]
 
     env:
       RAILS_ENV: test

.github/workflows/rspec_test.yml

@@ -14,7 +14,7 @@ jobs:
       fail-fast: false
       matrix:
         node: [22.x]
-        ruby: [3.4.6]
+        ruby: [3.4.3]
 
     services:
       postgres: