Move SSO clients from config to database

- Add sso_clients table (migration 000010) with client_id, redirect_uri,
  tags (JSON), enabled flag, and audit timestamps
- Add SSOClient model struct and audit events
- Implement DB CRUD with 10 unit tests
- Add REST API: GET/POST/PATCH/DELETE /v1/sso/clients (policy-gated)
- Add gRPC SSOClientService with 5 RPCs (admin-only)
- Add mciasctl sso list/create/get/update/delete commands
- Add web UI admin page at /sso-clients with HTMX create/toggle/delete
- Migrate handleSSOAuthorize and handleSSOTokenExchange to use DB
- Remove SSOConfig, SSOClient struct, lookup methods from config
- Simplify: client_id = service_name for policy evaluation

Security:
- SSO client CRUD is admin-only (policy-gated REST, requireAdmin gRPC)
- redirect_uri must use https:// (validated at DB layer)
- Disabled clients are rejected at both authorize and token exchange
- All mutations write audit events

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

web/templates/sso_clients.html

@@ -0,0 +1,53 @@
+{{define "title"}} - SSO Clients{{end}}
+{{define "content"}}
+<div class="page-header d-flex justify-between align-center">
+  <div>
+    <h2>SSO Clients</h2>
+    <p class="text-muted text-small">Registered applications that use MCIAS for single sign-on.</p>
+  </div>
+  <button class="btn btn-primary" onclick="var f=document.getElementById('create-form');f.hidden=!f.hidden;this.textContent=f.hidden?'Add Client':'Cancel'">Add Client</button>
+</div>
+
+<div id="create-form" class="card mt-2" hidden>
+  <div class="card-title">Register SSO Client</div>
+  <form hx-post="/sso-clients" hx-target="#sso-clients-tbody" hx-swap="afterbegin">
+    <div class="d-flex gap-1" style="flex-wrap:wrap">
+      <div class="form-group" style="flex:1;min-width:200px">
+        <label class="form-label">Client ID / Service Name</label>
+        <input class="form-control" type="text" name="client_id" required placeholder="e.g. mcr">
+      </div>
+      <div class="form-group" style="flex:2;min-width:300px">
+        <label class="form-label">Redirect URI</label>
+        <input class="form-control" type="url" name="redirect_uri" required placeholder="https://service.example.com/sso/callback">
+      </div>
+      <div class="form-group" style="flex:1;min-width:200px">
+        <label class="form-label">Tags <span class="text-muted text-small">(comma-separated)</span></label>
+        <input class="form-control" type="text" name="tags" placeholder="env:prod,tier:web">
+      </div>
+    </div>
+    <div class="form-actions">
+      <button class="btn btn-primary" type="submit">Create</button>
+    </div>
+  </form>
+</div>
+
+<div class="table-wrapper">
+  <table>
+    <thead>
+      <tr>
+        <th>Client ID</th>
+        <th>Redirect URI</th>
+        <th>Tags</th>
+        <th>Status</th>
+        <th>Actions</th>
+      </tr>
+    </thead>
+    <tbody id="sso-clients-tbody">
+      {{range .Clients}}
+      {{template "sso_client_row" .}}
+      {{end}}
+    </tbody>
+  </table>
+  {{if not .Clients}}<p class="text-muted" style="text-align:center;padding:2rem">No SSO clients registered.</p>{{end}}
+</div>
+{{end}}