feat: promote ContextWindowUsageBreakdown to stable

Enable the context_window_usage_breakdown Cargo feature by default and
remove the redundant DOGFOOD_FLAGS entry while keeping the runtime flag
and compile-time bridge for rollback.

Co-Authored-By: Oz <oz-agent@warp.dev>

Author: captainsafia

app/Cargo.toml

@@ -600,6 +600,7 @@ default = [
     "mcp_grouped_server_context",
     "fork_from_command",
     "context_window_usage_v2",
+    "context_window_usage_breakdown",
     "ambient_agents_command_line",
     "ambient_agents_image_upload",
     "scheduled_ambient_agents",

crates/warp_features/src/lib.rs

@@ -519,8 +519,8 @@ pub enum FeatureFlag {
     /// Enables v2 of the context window usage UI.
     ContextWindowUsageV2,
 
-    /// Dev-only: enables the expandable per-segment context window usage
-    /// breakdown in the conversation usage card.
+    /// Enables the expandable per-segment context window usage breakdown in
+    /// the conversation usage card.
     ContextWindowUsageBreakdown,
 
     /// Enables global search
@@ -1000,7 +1000,6 @@ pub const DOGFOOD_FLAGS: &[FeatureFlag] = &[
     FeatureFlag::WarpControlCli,
     FeatureFlag::TerminalLifecycleRecovery,
     FeatureFlag::PromptCacheExpiryWarning,
-    FeatureFlag::ContextWindowUsageBreakdown,
     FeatureFlag::JupyterNotebookRendering,
     FeatureFlag::WaitForEventsParentRegistration,
     FeatureFlag::McpJsonTreeView,