fix(sessions): title app-created sessions from the first user message

App-created sessions (started by sending a message from cloudcli) were
titled with placeholder names — "Untitled Codex Session" from the disk
indexer and, briefly, "New session" from the empty canonical upsert —
before a later sync finally settled on the right text, causing the
sidebar title to flicker.

- Codex/OpenCode synchronizers now title app-created sessions (distinct
  app id mapped to a provider id) from the first user message, while
  sessions found purely by indexing keep their existing setup. Claude
  keeps its AI-generated titles; Cursor already used the first message.
- Decode OpenCode's JSON-string-literal prompts so titles no longer
  surface wrapped in quotes; hoist unwrapJsonStringLiteral into
  shared/utils since it's now used by both the reader and synchronizer.
- Guard the sidebar upsert merge so an empty summary can never blank out
  a title that is already set.
- Add codex/opencode synchronizer tests for the app-created vs indexed
  naming paths.

server/modules/providers/list/opencode/opencode-sessions.provider.ts

@@ -14,6 +14,7 @@ import {
   readJsonRecord,
   readOptionalString,
   sliceTailPage,
+  unwrapJsonStringLiteral,
 } from '@/shared/utils.js';
 
 const PROVIDER = 'opencode';
@@ -60,25 +61,6 @@ const formatToolContent = (value: unknown): string => {
   }
 };
 
-/**
- * OpenCode can persist the first prompt as a JSON string literal inside a text
- * part, for example `"hello"` instead of `hello`. Decode only complete JSON
- * string literals so normal assistant/user prose remains untouched.
- */
-const unwrapJsonStringLiteral = (value: string): string => {
-  const trimmed = value.trim();
-  if (!trimmed.startsWith('"') || !trimmed.endsWith('"')) {
-    return value;
-  }
-
-  try {
-    const parsed = JSON.parse(trimmed);
-    return typeof parsed === 'string' ? parsed : value;
-  } catch {
-    return value;
-  }
-};
-
 const extractText = (value: unknown): string => {
   if (typeof value === 'string') {
     return unwrapJsonStringLiteral(value);