yavsc-org: OAuth2 client admin editor overhaul — per-collection pages + missing fields

The OAuth2 client editor at /Client/Edit/{id} previously exposed 8
fields out of ~30 scalars and 10 collections on the IdentityServer8
Client entity. Editing the collections (RedirectUris, Scopes, Grant
Types, Cors Origins, IdP Restrictions, Claims, Properties, Secrets)
was either impossible or jammed into a single broken text input that
bound against an IEnumerable<string> property.

Restructure into per-collection subpages, each with its own
list/add/remove flow:

- RedirectUris       /Client/EditRedirectUris/{id}
- PostLogoutRedirectUris /Client/EditPostLogoutRedirectUris/{id}
- Scopes             /Client/EditScopes/{id}
- GrantTypes         /Client/EditGrantTypes/{id}
- CorsOrigins        /Client/EditCorsOrigins/{id}
- IdPRestrictions    /Client/EditIdPRestrictions/{id}
- Claims             /Client/EditClaims/{id}
- Properties         /Client/EditProperties/{id}
- Secrets            /Client/EditSecrets/{id}

Implementation:

- New partial class ClientController.Collections.cs with one
  GET/Add/Remove trio per collection. Add/Remove dispatch through
  generic helpers that handle the EF row + ClientId check.
- Shared _EditableStringList.cshtml partial consumed by the six
  single-string-field collection pages. Uses reflection to pull
  the value field and the row Id off the entity — avoids six
  nearly-identical table+form copies.
- Claims / Properties / Secrets each have their own view because
  they carry 2+ fields (Type+Value, Key+Value, or
  Type+Value+Description+Expiration).
- Main Edit.cshtml enriched: ClientId/Id hidden, all scalar
  fields split into fieldsets (Core, Security, Logout, Tokens,
  Device flow, Tokens extra), nav links to the 9 subpages with
  current row counts as badges.
- ClientController.Edit(int) GET now loads the client with all
  navigations via LoadClientAsync so the Edit.cshtml nav badges
  render real counts.

Field-correctness notes (verified by disassembling HigginsSoft
IdentityServer8.EntityFramework.Entities.Client 8.0.5-preview-net9):

- The property is PairWiseSubjectSalt, not PairwiseSubjectSalt
  (capital W on 'Wise').
- CibaLifetime and PollingInterval do NOT exist on Client in this
  IdentityServer8 version — those properties were a guess. The
  Device flow fieldset contains DeviceCodeLifetime + UserCodeType
  instead.
- AllowedIdentityTokenSigningAlgorithms and AllowAccessTokensViaBrowser
  were missing from the original form and are now exposed.
- ConsentLifetime and UserSsoLifetime are int? (nullable); the form
  binds them as plain int fields which accept empty strings.

Security:

- All new actions stay under [Authorize('AdministratorOnly')].
- Each Add/Remove takes an explicit id (Client.Id) and the row's
  ClientId is checked on the server before any delete; a rowId
  from another client returns NotFound.

Docs:

- doc/dev-tracking/client-editor-overhaul.md — inventory, status,
  follow-up ideas (confirmation prompts, validation, MVC tests).

src/Yavsc.Org/Controllers/Administration/ClientController.cs

@@ -13,7 +13,7 @@ using Yavsc.Server.Helpers;
 namespace Yavsc.Controllers
 {
     [Authorize("AdministratorOnly")]
-    public class ClientController : Controller
+    public partial class ClientController : Controller
     {
         private readonly ApplicationDbContext dbContext;
         private readonly ClientStore clientStore;
@@ -137,8 +137,8 @@ namespace Yavsc.Controllers
         // GET: Client/Edit/5
         public async Task<IActionResult> Edit(int id)
         {
-            Client client = await dbContext.Clients.SingleOrDefaultAsync(m => m.Id == id);
-            if (client == null)
+            Client? client = await LoadClientAsync(id);
+            if (client is null)
             {
                 return NotFound();
             }