Rename "Fork from here" to "Fork from here (dev only)" (warpdotdev#9941)

## Description

Renames the "Fork from here" context menu item to "Fork from here (dev
only)" to make it clear this is a dev/dogfood-only debugging tool and
not a user-facing feature.

This item (which triggers `ForkAIConversationFromExactExchange`) is
already gated behind `is_dogfood()`, so it's never shown to
preview/stable users. The new label clarifies the intent to anyone on
the dogfood channel who sees it.

## Linked Issue

N/A — minor label clarification requested via Slack feedback.

- [ ] The linked issue is labeled `ready-to-spec` or
`ready-to-implement`.
- [x] Where appropriate, screenshots or a short video of the
implementation are included below (especially for user-visible or UI
changes).

## Testing

Label-only change; no logic changes. The item remains gated behind
`ChannelState::channel().is_dogfood()`.

## Agent Mode
- [x] Warp Agent Mode - This PR was created via Warp's AI Agent Mode

_Conversation:
https://staging.warp.dev/conversation/89fa5f8f-458c-4613-9f43-fd1c4f5d0d66_
_Run:
https://oz.staging.warp.dev/runs/019deacc-8b29-70d0-a676-c4d591420ba2_

_This PR was generated with [Oz](https://warp.dev/oz)._

Co-authored-by: Oz <oz-agent@warp.dev>

Author: zachlloyd

app/src/terminal/view.rs

@@ -15510,7 +15510,7 @@ impl TerminalView {
 
                             if ChannelState::channel().is_dogfood() {
                                 items.push(
-                                    MenuItemFields::new("Fork from here")
+                                    MenuItemFields::new("Fork from here (dev only)")
                                         .with_on_select_action(TerminalAction::ContextMenu(
                                             ContextMenuAction::ForkAIConversationFromExactExchange {
                                                 ai_block_view_id: *rich_content_view_id,
@@ -16511,7 +16511,7 @@ impl TerminalView {
 
             if ChannelState::channel().is_dogfood() {
                 menu_items.push(
-                    MenuItemFields::new("Fork from here")
+                    MenuItemFields::new("Fork from here (dev only)")
                         .with_on_select_action(TerminalAction::ContextMenu(
                             ContextMenuAction::ForkAIConversationFromExactExchange {
                                 ai_block_view_id,