Reorganise codebase: EffectiveConfig, parsers, tests; move tooltips to Metadata

Infrastructure:
- Parsers under Serialization/Parsers: Dnsmasq, DnsmasqConfig, EffectiveConfig
- EffectiveConfig: Abstractions, Metadata (keys, views, field builder, tooltips,
  placeholders, write semantics), Rendering, Editing, Validation/Handlers, Readonly
- Helpers/Config: only DnsmasqFileEncoding; DnsmasqOptionTooltips moved to Metadata
- Remove empty Infrastructure/Parsers and Helpers/Dnsmasq

Tests:
- Mirror main project: Serialization/Parsers (Dnsmasq, DnsmasqConfig),
  Services/Dnsmasq/Config, Services/EffectiveConfig, Models, Helpers (TestDataHelper)
- Namespaces updated; usings for TestDataHelper and Metadata where needed

Docs: README codebase overview and test layout updated.

src/DnsmasqWebUI/Components/EffectiveConfig/Composition/EffectiveConfigPanels.razor

@@ -1,7 +1,6 @@
 @namespace DnsmasqWebUI.Components.EffectiveConfig
 @using DnsmasqWebUI.Models.Dnsmasq
 @using DnsmasqWebUI.Models.Dnsmasq.EffectiveConfig
-@using DnsmasqWebUI.Infrastructure.Helpers.Config
 @inject IEffectiveConfigRenderFragmentRegistry RenderFragmentRegistry
 
 <div class="ec-sections small">

src/DnsmasqWebUI/Components/EffectiveConfig/Composition/EffectiveConfigSection.razor

@@ -1,7 +1,6 @@
 @namespace DnsmasqWebUI.Components.EffectiveConfig
 @using DnsmasqWebUI.Models.Dnsmasq
 @using DnsmasqWebUI.Models.Dnsmasq.EffectiveConfig
-@using DnsmasqWebUI.Infrastructure.Helpers.Config
 @using DnsmasqWebUI.Infrastructure.Services.EffectiveConfig.Abstractions
 @using DnsmasqWebUI.Infrastructure.Services.EffectiveConfig.Validation
 @inject IEffectiveConfigEditSession Session

src/DnsmasqWebUI/Components/EffectiveConfig/CustomDisplays/KeyOnlyOrValueDisplay.razor

@@ -1,5 +1,4 @@
 @namespace DnsmasqWebUI.Components.EffectiveConfig.CustomDisplays
-@using DnsmasqWebUI.Infrastructure.Helpers.Config
 @using DnsmasqWebUI.Models.Dnsmasq
 @inherits EffectiveConfigValueDisplayBase
 

src/DnsmasqWebUI/Components/EffectiveConfig/Fields/EffectiveConfigFieldDisplay.razor

@@ -2,7 +2,6 @@
 @using DnsmasqWebUI.Models.Dnsmasq
 @using DnsmasqWebUI.Models.Dnsmasq.EffectiveConfig
 @using DnsmasqWebUI.Models.Config
-@using DnsmasqWebUI.Infrastructure.Helpers.Config
 @using DnsmasqWebUI.Infrastructure.Services.EffectiveConfig.Abstractions
 @using DnsmasqWebUI.Infrastructure.Services.UI.Notifications.Abstractions
 @inject IEffectiveConfigRenderFragmentRegistry RenderFragmentRegistry

src/DnsmasqWebUI/Components/EffectiveConfig/Fields/EffectiveConfigMultiValueListEditor.razor

@@ -1,5 +1,4 @@
 @namespace DnsmasqWebUI.Components.EffectiveConfig
-@using DnsmasqWebUI.Infrastructure.Helpers.Config
 @using DnsmasqWebUI.Models.Dnsmasq
 @using DnsmasqWebUI.Models.Dnsmasq.EffectiveConfig
 @using Microsoft.AspNetCore.Components.Web

src/DnsmasqWebUI/Components/EffectiveConfig/Fields/EffectiveConfigOptionItem.razor

@@ -1,5 +1,4 @@
 @namespace DnsmasqWebUI.Components.EffectiveConfig
-@using DnsmasqWebUI.Infrastructure.Helpers.Config
 @using DnsmasqWebUI.Models.Dnsmasq
 @using DnsmasqWebUI.Models.Dnsmasq.EffectiveConfig
 

src/DnsmasqWebUI/Components/EffectiveConfig/Modals/EffectiveConfigSaveModal.razor

@@ -2,7 +2,6 @@
 @using DnsmasqWebUI.Models.Dnsmasq
 @using DnsmasqWebUI.Models.Dnsmasq.EffectiveConfig
 @using DnsmasqWebUI.Infrastructure.Services.EffectiveConfig.Abstractions
-@using DnsmasqWebUI.Infrastructure.Helpers.Config
 
 <div class="modal fade show" style="display: block;" tabindex="-1" role="dialog" aria-labelledby="ec-save-modal-title" aria-modal="true">
     <div class="modal-dialog modal-dialog-scrollable" role="document">

src/DnsmasqWebUI/Components/EffectiveConfig/Popovers/ReadonlyEditHint.razor

@@ -1,6 +1,5 @@
 @namespace DnsmasqWebUI.Components.EffectiveConfig
 @using DnsmasqWebUI.Models.Dnsmasq.EffectiveConfig
-@using DnsmasqWebUI.Infrastructure.Helpers.Config
 
 @if (Source is { IsReadOnly: true })
 {

src/DnsmasqWebUI/Components/EffectiveConfig/Popovers/ReadonlyEditPopover.razor

@@ -1,6 +1,5 @@
 @namespace DnsmasqWebUI.Components.EffectiveConfig
 @using DnsmasqWebUI.Models.Dnsmasq.EffectiveConfig
-@using DnsmasqWebUI.Infrastructure.Helpers.Config
 @using DnsmasqWebUI.Extensions
 @using Microsoft.AspNetCore.Components
 @using Microsoft.JSInterop