Phase 003: remove the coding-agent and ekko-agent runtimes

Every chat session now runs through the Hermes bridge, so the three chat
chains become feature-equivalent instead of three partially-maintained
dispatch paths. Keeping the coding-agent and in-house agent runtimes alive
meant every bridge change had to be mirrored into two more runtimes that
had already drifted.

Historical rows are read, not migrated: sessions stored with the retired
source normalize to cli on load, workflow graphs naming the retired agents
keep loading and run on the bridge, and the visible-source check plus
SOURCE_LABELS still recognize the old value so those sessions stay listed.

The public surface follows the code: the OpenAPI generator and the MCP
chat-run tool schema drop the six retired entry fields so external callers
are not told about runtimes that no longer exist.

harness-check gains a RETIRED_RUNTIME scan so the residual check is a
mechanical gate instead of a manual grep, with the two surviving read-side
compat sites recorded with reasons.

Refs: docs/phases/phase_003.md

packages/client/src/components/layout/AppSidebar.vue

@@ -259,14 +259,6 @@ function handleUpdateClick() {
           </svg>
         </div>
         <div v-show="!isGroupCollapsed('tools')" class="nav-group-items">
-          <RouteLinkItem v-if="hasRoute('hermes.codingAgents')" class="nav-item" :to="{ name: 'hermes.codingAgents' }" :active="selectedKey === 'hermes.codingAgents'">
-            <svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round">
-              <polyline points="16 18 22 12 16 6" />
-              <polyline points="8 6 2 12 8 18" />
-              <line x1="12" y1="20" x2="14" y2="4" />
-            </svg>
-            <span>{{ t("sidebar.codingAgents") }}</span>
-          </RouteLinkItem>
           <RouteLinkItem v-if="hasRoute('hermes.versionPreview') && isSuperAdmin && !isVersionPreview" class="nav-item" :to="{ name: 'hermes.versionPreview' }" :active="selectedKey === 'hermes.versionPreview'">
             <svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round">
               <path d="M21 16V8a2 2 0 0 0-1-1.73l-7-4a2 2 0 0 0-2 0l-7 4A2 2 0 0 0 3 8v8a2 2 0 0 0 1 1.73l7 4a2 2 0 0 0 2 0l7-4A2 2 0 0 0 21 16z" />