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

scripts/extract-option-help.sh

@@ -216,7 +216,9 @@ OPTION_KEYS = [
     "dumpmask",
     "use-stale-cache",
     "add-mac",
+    "strip-mac",
     "add-subnet",
+    "strip-subnet",
     "umbrella",
     "quiet-dhcp",
     "quiet-dhcp6",