feat(sv-ui): render and propose a RegisterSynchronizer vote

[timwu20]

Closes ChainSafe/canton-extending-mainnet#121

Stacked on #47, which adds the governance parameters to the registration choice.

Summary: the SV governance UI can now display and propose a SRARC_RegisterSynchronizer
vote. Two commits, because the first is a defect fix on its own.

Render (83c7834). The UI's action list is a closed union, so a registration vote was
an unknown action to it: voteRequestDetails returned "Error, something went wrong.
Unsupported Action: SRARC_RegisterSynchronizer" and the listing showed an undefined action
name. Every SV asked to vote on a registration saw a broken row and an error page instead
of the synchronizer id and operator it was approving. The detail view now shows the
synchronizer id, the operator, and the traffic discount the registration would carry.

Propose (ee91987). A registration vote had to be assembled as an
ActionRequiringConfirmation through the API, which is what
LocalNetDedicatedSyncIntegrationTest does. The create-proposal page now offers
"Register Dedicated Synchronizer" and builds the same action that test constructs.

Two checks the form adds beyond the Daml choice, which only requires a non-empty id:

• the synchronizer id must be name::fingerprint, the shape agreed on the design doc
  thread
• the traffic discount, if given, must be in (0, 1], matching the template's ensure.
  Leaving it empty registers at the full price

Setting the discount here is the point of the stack: the proposal that registers a
synchronizer carries the parameters it is registered with, so an agreed discount does not
need a second vote while the synchronizer runs at full price.

How it's verified

apps-common-frontend/npmTest green, including a new
register-synchronizer-form.test.tsx: fields render, an empty form reports its required
fields and re-enables submit once filled with the discount left empty, a malformed
synchronizer id is rejected, and 1.5 is rejected where 0.5 is accepted.
apps-frontends/npmLint green.

Not in scope: the duplicate-id warning, which needs a Scan client in the SV frontend
(ChainSafe/canton-extending-mainnet#54).