Effective config: no-0x20 precedence, write semantics, validators, strip-mac/strip-subnet

- ConfigSetCache: no-0x20-encode wins per dnsmasq docs; effective state and source attribution updated
- ReadonlyConfigCommandGenerator: use EffectiveConfigWriteSemantics for inverse-pair and key-only-or-value
- SpecialOptionValidators for UseStaleCache, AddMac, AddSubnet, Umbrella; wired via RegisterValidatedSingle
- OptionSemantics + EffectiveConfigWriteSemantics (GetBehavior/GetInversePairKeys); remove EffectiveConfigWriteBehaviorMap
- strip-mac / strip-subnet: full support in EffectiveDnsmasqConfig, sources, cache, sections, field builder, registry, tests
- Multi-value editor: toasts and block commit on validation error; 2s toast dedupe
- Do0x20 view label comment + Do0x20EncodeDisplayLabelTests
- DnsmasqOptionTooltips + extract-option-help.sh for strip-mac/strip-subnet; regenerated option-help HTML

src/DnsmasqWebUI/Components/EffectiveConfig/CustomDisplays/Do0x20EncodeDisplay.razor

@@ -11,6 +11,7 @@
 }
 else
 {
+    @* Intentionally show both Default and Disabled as "Disabled" (product choice: collapse unset and off). Do not "fix" to show "Default" for unset. *@
     @(GetState() == ExplicitToggleState.Enabled ? "Enabled" : "Disabled")
 }