Split data layer into btcdata service

Remove DB, Binance WebSocket, and Kraken pollers from btcprice.
UI now uses vanilla EventSource connecting to btcdata for live
price updates. btcprice is now a pure UI service with no database.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

deps.edn

@@ -1,7 +1,5 @@
 {:paths ["src/clj" "resources"]
  :deps {org.clojure/clojure                  {:mvn/version "1.12.3"}
-        org.clojure/data.json                {:mvn/version "2.5.1"}
-
         ;; Kit
         io.github.kit-clj/kit-core           {:mvn/version "1.0.6"}
 
@@ -27,12 +25,7 @@
 
         ;; Serialization
         metosin/muuntaja                     {:mvn/version "0.6.11"}
-        luminus-transit/luminus-transit       {:mvn/version "0.1.6"}
-
-        ;; Database
-        io.github.kit-clj/kit-postgres       {:mvn/version "1.0.7"}
-        io.github.kit-clj/kit-sql-conman     {:mvn/version "1.10.5"}
-        io.github.kit-clj/kit-sql-migratus   {:mvn/version "1.0.5"}}
+        luminus-transit/luminus-transit       {:mvn/version "0.1.6"}}
 
  :aliases
  {:build {:deps {io.github.clojure/tools.build {:mvn/version "0.10.9"}}