[E7-1] Make `fees` per-synchronizer in `AmuletConfig`

[salindne]

Turn the single global SynchronizerFeesConfig into a per-sync map; ripples into validators, all three Patchable instances, and both fee-computation sites. Large blast radius: ~60 Scala + ~50 TS consumers (most read-only), plus the SV governance UI config builders.

Key files: DecentralizedSynchronizer.daml:21/:36, Patchable :179/:184/:192; AmuletConfig.daml:97; apps/common/.../util/SpliceUtil.scala:507; cluster/pulumi/common/src/domainFees.ts; apps/sv/frontend/src/utils/buildAmuletConfigChanges.ts

Acceptance criteria:

• Fees can differ per synchronizer; governance can set a dedicated sync's rate by vote
• Codegen + Scala + TS consumers compile; SV config UI round-trips the new shape

Epic: #10

Source: docs/planning/extending-mainnet-work-plan.md