Separate OpenCode and Public model management in admin panel

- Add OpenCode Models section with dropdown selection from available models
- Add Public Models section with manual model ID input
- Both sections have up/down ordering buttons for fallback chain priority
- OpenCode models used for execution fallback when rate limits/errors occur
- Public models displayed in builder dropdown for user selection
- Remove unified provider chain in favor of two separate lists
- Keep all existing functionality: Auto Model, Provider Limits, Icon Library, etc.

chat/server.js

@@ -11320,8 +11320,9 @@ async function processMessage(sessionId, message) {
 
 function getConfiguredModels(cliParam = 'opencode') {
   const cli = normalizeCli(cliParam || 'opencode');
-  // Return opencode models for backwards compatibility
-  const mapped = opencodeModels.map((m, idx) => ({
+  // Return public models for user-facing dropdown selection
+  // These are the models displayed to users in the builder
+  const mapped = publicModels.map((m, idx) => ({
     id: m.id,
     name: m.name,
     label: m.label || m.name,
@@ -11336,6 +11337,20 @@ function getConfiguredModels(cliParam = 'opencode') {
   return mapped;
 }
 
+function getOpencodeModelsForExecution() {
+  // Return opencode models for internal fallback chain during execution
+  // These models are used when rate limits are reached or errors occur
+  return opencodeModels.map((m) => ({
+    id: m.id,
+    name: m.name,
+    label: m.label || m.name,
+    icon: m.icon || '',
+    tier: m.tier || 'free',
+    multiplier: getTierMultiplier(m.tier || 'free'),
+    supportsMedia: m.supportsMedia ?? false,
+  }));
+}
+
 async function handleModels(_req, res, cliParam = null) {
   try {
     const models = getConfiguredModels(cliParam || 'opencode');