Clarify first-run login onboarding and conditional auth messaging across Web/Desktop

[Copilot]

This change makes first-run account creation explicit (first user becomes admin), removes irrelevant auth UI states, and adds in-flight progress feedback during sign-in/registration. It aligns Web and Desktop login behavior so users only see messages/actions that apply to their current server state.

• First-run onboarding clarity

  • Web and Desktop now show a dedicated first-run explainer that states the first created account is the administrator.
  • First-run primary action is explicitly “Create administrator account” (instead of generic sign-in/register affordances).

• State-driven messaging and actions

  • Registration section is shown only when registration is open and first-run is complete.
  • Approval requirement note is shown only when approval is actually required.
  • “Pending approval” is surfaced as informational success-style feedback instead of an error state.

• Progress feedback during auth operations

  • Added busy status label + spinner/progress indicators while login/registration is in flight.
  • Inputs and auth actions are disabled while busy to prevent duplicate submissions.
  • Busy labels are operation-specific (sign-in vs account/admin-account creation).

• Role correctness on post-registration sign-in path

  • Web and Desktop continue to honor the role returned by identity service for the new account (no implicit admin elevation outside first registrant path).

public bool ShowRegistrationSection => !IsFirstRun && IsRegistrationOpen;

if (result.IsPendingApproval)
{
    InfoMessage = "Account created. An administrator must approve it before you can sign in.";
    return;
}

[Copilot]

Pull request overview

This PR updates the Web (Blazor) and Desktop (Avalonia) login experiences to be more state-driven: clearly distinguishing first-run onboarding (first user becomes admin), hiding irrelevant registration/approval messaging, and adding in-flight progress feedback during sign-in/registration.

Changes:

• Added explicit first-run onboarding messaging and a dedicated “Create administrator account” primary action.
• Made registration/approval UI conditional on server state, and surfaced “pending approval” as informational feedback instead of an error.
• Added busy/progress indicators and disabled inputs/actions while auth operations are in flight.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
src/Sovrant.Web/wwwroot/css/sovrant.css	Adds styles for first-run info box, success/info messaging, and busy status/spinner.
src/Sovrant.Web/Components/Pages/Login.razor	Implements first-run explainer/action, conditional registration + approval note, and busy status UI.
src/Sovrant.Desktop/Views/LoginWindow.axaml	Aligns Desktop login UI with first-run/conditional messaging and adds busy label display.
src/Sovrant.Desktop/ViewModels/LoginViewModel.cs	Adds state-driven properties/messages and operation-specific busy labels for login/register flows.

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