feat: add session info panel with message count, context usage, cache stats, and skills

Add GET /bots/:bot_id/sessions/:session_id/info API endpoint that returns
per-session message count, latest input token usage with model context window,
aggregated KV cache hit rate, and skills invoked via use_skill tool calls.
Frontend Info tab in the right sidebar now displays this data in a compact
key-value layout with a context usage progress bar and clickable skill links.

cmd/agent/main.go

@@ -256,6 +256,7 @@ func runServe() {
 			provideServerHandler(handlers.NewMCPOAuthHandler),
 			provideOAuthService,
 			provideServerHandler(handlers.NewTokenUsageHandler),
+			provideServerHandler(handlers.NewSessionInfoHandler),
 			provideServerHandler(handlers.NewBrowserContextsHandler),
 			provideServerHandler(handlers.NewSupermarketHandler),
 			provideServerHandler(provideCLIHandler),

cmd/memoh/serve.go

@@ -183,6 +183,7 @@ func runServe() {
 			provideServerHandler(handlers.NewMCPOAuthHandler),
 			provideOAuthService,
 			provideServerHandler(handlers.NewTokenUsageHandler),
+			provideServerHandler(handlers.NewSessionInfoHandler),
 			provideServerHandler(handlers.NewBrowserContextsHandler),
 			provideServerHandler(provideCLIHandler),
 			provideServerHandler(provideWebHandler),