feat: add database tables and API routes for agentic chat feature (#17570)

Backend portion of experimental `AgenticChat` feature:
- Adds database tables for chats and chat messages
- Adds functionality to stream messages from LLM providers using
`kylecarbs/aisdk-go`
- Adds API routes with relevant functionality (list, create, update
chats, insert chat message)
- Adds experiment `codersdk.AgenticChat`

---------

Co-authored-by: Kyle Carberry <kyle@carberry.com>

coderd/coderd.go

@@ -41,6 +41,7 @@ import (
 	"github.com/coder/quartz"
 	"github.com/coder/serpent"
 
+	"github.com/coder/coder/v2/coderd/ai"
 	"github.com/coder/coder/v2/coderd/cryptokeys"
 	"github.com/coder/coder/v2/coderd/entitlements"
 	"github.com/coder/coder/v2/coderd/files"
@@ -155,6 +156,7 @@ type Options struct {
 	Authorizer                     rbac.Authorizer
 	AzureCertificates              x509.VerifyOptions
 	GoogleTokenValidator           *idtoken.Validator
+	LanguageModels                 ai.LanguageModels
 	GithubOAuth2Config             *GithubOAuth2Config
 	OIDCConfig                     *OIDCConfig
 	PrometheusRegistry             *prometheus.Registry
@@ -851,7 +853,7 @@ func New(options *Options) *API {
 				next.ServeHTTP(w, r)
 			})
 		},
-		httpmw.CSRF(options.DeploymentValues.HTTPCookies),
+		// httpmw.CSRF(options.DeploymentValues.HTTPCookies),
 	)
 
 	// This incurs a performance hit from the middleware, but is required to make sure
@@ -956,6 +958,7 @@ func New(options *Options) *API {
 			r.Get("/config", api.deploymentValues)
 			r.Get("/stats", api.deploymentStats)
 			r.Get("/ssh", api.sshConfig)
+			r.Get("/llms", api.deploymentLLMs)
 		})
 		r.Route("/experiments", func(r chi.Router) {
 			r.Use(apiKeyMiddleware)
@@ -998,6 +1001,21 @@ func New(options *Options) *API {
 			r.Get("/{fileID}", api.fileByID)
 			r.Post("/", api.postFile)
 		})
+		// Chats are an experimental feature
+		r.Route("/chats", func(r chi.Router) {
+			r.Use(
+				apiKeyMiddleware,
+				httpmw.RequireExperiment(api.Experiments, codersdk.ExperimentAgenticChat),
+			)
+			r.Get("/", api.listChats)
+			r.Post("/", api.postChats)
+			r.Route("/{chat}", func(r chi.Router) {
+				r.Use(httpmw.ExtractChatParam(options.Database))
+				r.Get("/", api.chat)
+				r.Get("/messages", api.chatMessages)
+				r.Post("/messages", api.postChatMessages)
+			})
+		})
 		r.Route("/external-auth", func(r chi.Router) {
 			r.Use(
 				apiKeyMiddleware,