Fix data races across session/forwarder/registry, resolve POST/PUT hang, harden port allocation, add frontendURL env (#157)

Reviewed-on: #157
Co-authored-by: Bagas <bagas@fossy.my.id>
Co-committed-by: Bagas <bagas@fossy.my.id>

internal/session/interaction/interaction_test.go

@@ -32,6 +32,7 @@ type MockConfig struct {
 }
 
 func (m *MockConfig) Domain() string            { return m.Called().String(0) }
+func (m *MockConfig) FrontendURL() string       { return m.Called().String(0) }
 func (m *MockConfig) SSHPort() string           { return m.Called().String(0) }
 func (m *MockConfig) HTTPPort() string          { return m.Called().String(0) }
 func (m *MockConfig) HTTPSPort() string         { return m.Called().String(0) }