feat: make Coder Agents right sidebar app and port tabs generally available (#26906)

The workspace-app and port preview tabs in the Coder Agents right panel
were gated behind the `agent-app-tabs` deployment experiment. This
removes the experiment entirely and renders the app and port tabs
unconditionally, so the add-panel dropdown, workspace-app tabs, and port
preview tabs are always available alongside terminals.

## Changes

- Remove the `ExperimentAgentAppTabs` constant, its `DisplayName()`
case, and its `ExperimentsKnown` registration in
`codersdk/deployment.go`, then regenerate
`site/src/api/typesGenerated.ts`, `coderd/apidoc/docs.go`,
`coderd/apidoc/swagger.json`, and `docs/reference/api/schemas.md`.
- Drop the frontend experiment gate in `AgentChatPageView.tsx`
(including the now-unused `useDashboard`/`experiments` usage) so
persisted app and port tabs are no longer filtered out.
- Remove the `appExperimentEnabled` prop from `RightPanelAddTabControl`
and render the add-panel dropdown unconditionally; update the stories
accordingly.

This reverses the gating introduced in #26395.

note: the diff is tiny if you hide whitespace changes

coderd/apidoc/docs.go

@@ -19630,13 +19630,11 @@ const docTemplate = `{
                 "nats_pubsub",
                 "minimum-implicit-member",
                 "ai-gateway-cost-control",
-                "agent-app-tabs",
                 "chat-advisor",
                 "chat-virtual-desktop"
             ],
             "x-enum-comments": {
                 "ExperimentAIGatewayCostControl": "Enables AI Gateway cost control functionality.",
-                "ExperimentAgentAppTabs": "Enables workspace-app and port preview tabs in the Coder Agents right panel.",
                 "ExperimentAutoFillParameters": "This should not be taken out of experiments until we have redesigned the feature.",
                 "ExperimentChatAdvisor": "Enables the advisor tool for root agent chats.",
                 "ExperimentChatVirtualDesktop": "Enables virtual desktop and computer use provider for agents.",
@@ -19660,7 +19658,6 @@ const docTemplate = `{
                 "Enables embedded NATS pubsub.",
                 "Allows organizations to deviate from the default organization-member roles, in support of Gateway Accounts.",
                 "Enables AI Gateway cost control functionality.",
-                "Enables workspace-app and port preview tabs in the Coder Agents right panel.",
                 "Enables the advisor tool for root agent chats.",
                 "Enables virtual desktop and computer use provider for agents."
             ],
@@ -19675,7 +19672,6 @@ const docTemplate = `{
                 "ExperimentNATSPubsub",
                 "ExperimentMinimumImplicitMember",
                 "ExperimentAIGatewayCostControl",
-                "ExperimentAgentAppTabs",
                 "ExperimentChatAdvisor",
                 "ExperimentChatVirtualDesktop"
             ]

coderd/apidoc/swagger.json

@@ -17823,13 +17823,11 @@
 				"nats_pubsub",
 				"minimum-implicit-member",
 				"ai-gateway-cost-control",
-				"agent-app-tabs",
 				"chat-advisor",
 				"chat-virtual-desktop"
 			],
 			"x-enum-comments": {
 				"ExperimentAIGatewayCostControl": "Enables AI Gateway cost control functionality.",
-				"ExperimentAgentAppTabs": "Enables workspace-app and port preview tabs in the Coder Agents right panel.",
 				"ExperimentAutoFillParameters": "This should not be taken out of experiments until we have redesigned the feature.",
 				"ExperimentChatAdvisor": "Enables the advisor tool for root agent chats.",
 				"ExperimentChatVirtualDesktop": "Enables virtual desktop and computer use provider for agents.",
@@ -17853,7 +17851,6 @@
 				"Enables embedded NATS pubsub.",
 				"Allows organizations to deviate from the default organization-member roles, in support of Gateway Accounts.",
 				"Enables AI Gateway cost control functionality.",
-				"Enables workspace-app and port preview tabs in the Coder Agents right panel.",
 				"Enables the advisor tool for root agent chats.",
 				"Enables virtual desktop and computer use provider for agents."
 			],
@@ -17868,7 +17865,6 @@
 				"ExperimentNATSPubsub",
 				"ExperimentMinimumImplicitMember",
 				"ExperimentAIGatewayCostControl",
-				"ExperimentAgentAppTabs",
 				"ExperimentChatAdvisor",
 				"ExperimentChatVirtualDesktop"
 			]