Fix cloud session title not applied when opening in chat panel

[Copilot]

Cloud sessions opened from the Agent Sessions list show the wrong title (e.g., "Initial Implementation" instead of the descriptive title). The title.preferred option was applied in the editor path (ChatEditor.setInput) but ignored in the panel path (chatView.loadSession), which is the default target.

Added the missing setChatSessionTitle call after loadSession in ChatWidgetService.openSession for the panel path, gated to non-local sessions — mirroring the existing editor path logic.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Different cloud session titles in Agent Sessions vs chat tab</issue_title>
<issue_description>

Ref https://github.com/microsoft/vscode-internalbacklog/issues/6527, perhaps similar to https://github.com/microsoft/vscode-internalbacklog/issues/6026

• code-insiders --transient
• Setup Copilot
• Review my sessions from the Agent Sessions list
• Click on a session Add cloud storage service example with... from Agent Sessions list
  • 
• ❓ The session title and prompt in the now open chat panel tab is Initial Implementation, rather than Add cloud storage service example with...
  • 
• ❓ I explore other cloud sessions, and I run into the same, where the session name in the Agent Sessions list is more descriptive, but the content (prompt and title) in the chat panel just ends up being Initial Implementation

I wonder if this could be a consequence of #286335 (cc @bpasero) </issue_description>

Comments on the Issue (you are @copilot in this section)

@bamurtaugh I also seem to experience this to some extent for background agents:

• Kick off a background agent task asking the agent to add a theme toggle to my app, let it run
• At some point, the task title in the Agent Sessions view became Start implementation (or maybe it was the whole time?)
  • 
• When clicking on the background session, the prompt is formatted with an extra Start implementation prepended (that I hadn't written)
  • </comment_new>
    <comment_new>@roblourens
    Details from me in ChatModel doesn't get the correct title for cloud sessions #290190</comment_new>
    <comment_new>@joaomoreno
    @joshspicer @rebornix Please fix this.

Duplicates:

• Cloud sessions show the wrong title when open #289910
• ChatModel doesn't get the correct title for cloud sessions #290190</comment_new>

• Fixes Different cloud session titles in Agent Sessions vs chat tab #286797

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