Add included agents in extensions search (#41679)

Given agent servers will soon be a thing, I'm adding Claude Code, Gemini
CLI, and Codex CLI as included agents in case anyone comes first to
search them as extensions before looking up on the agent panel.

Release Notes:

- N/A

crates/extensions_ui/src/extensions_ui.rs

@@ -225,6 +225,9 @@ impl ExtensionFilter {
 
 #[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Copy)]
 enum Feature {
+    AgentClaude,
+    AgentCodex,
+    AgentGemini,
     ExtensionRuff,
     ExtensionTailwind,
     Git,
@@ -244,6 +247,9 @@ fn keywords_by_feature() -> &'static BTreeMap<Feature, Vec<&'static str>> {
     static KEYWORDS_BY_FEATURE: OnceLock<BTreeMap<Feature, Vec<&'static str>>> = OnceLock::new();
     KEYWORDS_BY_FEATURE.get_or_init(|| {
         BTreeMap::from_iter([
+            (Feature::AgentClaude, vec!["claude", "claude code"]),
+            (Feature::AgentCodex, vec!["codex", "codex cli"]),
+            (Feature::AgentGemini, vec!["gemini", "gemini cli"]),
             (Feature::ExtensionRuff, vec!["ruff"]),
             (Feature::ExtensionTailwind, vec!["tail", "tailwind"]),
             (Feature::Git, vec!["git"]),
@@ -1422,6 +1428,24 @@ impl ExtensionsPage {
 
         for feature in &self.upsells {
             let banner = match feature {
+                Feature::AgentClaude => self.render_feature_upsell_banner(
+                    "Claude Code support is built-in to Zed!".into(),
+                    "https://zed.dev/docs/ai/external-agents#claude-code".into(),
+                    false,
+                    cx,
+                ),
+                Feature::AgentCodex => self.render_feature_upsell_banner(
+                    "Codex CLI support is built-in to Zed!".into(),
+                    "https://zed.dev/docs/ai/external-agents#codex-cli".into(),
+                    false,
+                    cx,
+                ),
+                Feature::AgentGemini => self.render_feature_upsell_banner(
+                    "Gemini CLI support is built-in to Zed!".into(),
+                    "https://zed.dev/docs/ai/external-agents#gemini-cli".into(),
+                    false,
+                    cx,
+                ),
                 Feature::ExtensionRuff => self.render_feature_upsell_banner(
                     "Ruff (linter for Python) support is built-in to Zed!".into(),
                     "https://zed.dev/docs/languages/python#code-formatting--linting".into(),