feat: add shared integration test framework for garages (#126)

Implements:
- BattleResult type and JSON-lines parser (#127)
- TR server lifecycle manager (#128)
- Bot compiler using nim c (#129)
- runBattle() orchestrator (#130)
- Example test in OscillatorBot_garage (#131)
- Framework usage guide (#132)
- TestBattleRunner.java for external server (#133)
- BattleRunner process lifecycle (#134)

Fix: runner_process.nim was redefining TimeoutError locally; now
uses std/net.TimeoutError consistently with server_manager.nim.

common_libs/test_framework/server_manager.nim

@@ -0,0 +1,67 @@
+## TR server lifecycle manager — lazy singleton for integration tests.
+## Start with ensureServer(), query with getServerUrl().
+
+import std/[osproc, net, os, strutils, times, streams, exitprocs]
+
+const
+  DefaultJar = "/home/davide/Projects/tank-royale/server/build/libs/robocode-tankroyale-server-0.35.5-all.jar"
+  ReadySignal = "Starting server on port"
+  StartupTimeout = 15.0  # seconds
+
+var
+  serverProc: Process = nil
+  serverPort: int = 0
+
+proc findFreePort(): int =
+  let s = newSocket()
+  s.bindAddr(Port(0))
+  let (_, port) = s.getLocalAddr()
+  result = port.int
+  s.close()
+
+proc ensureServer*() =
+  if serverProc != nil: return
+
+  let jar = getEnv("TR_SERVER_JAR", DefaultJar)
+  if not fileExists(jar):
+    raise newException(IOError, "TR server JAR not found: " & jar &
+      "\nSet TR_SERVER_JAR env var to override.")
+
+  serverPort = findFreePort()
+  serverProc = startProcess("java",
+    args = @["-jar", jar, "--port", $serverPort, "--enable-initial-position"],
+    options = {poUsePath, poStdErrToStdOut})
+
+  exitprocs.addExitProc(proc() =
+    if serverProc != nil:
+      serverProc.terminate()
+      serverProc.close()
+  )
+
+  # Wait for ready signal
+  let deadline = epochTime() + StartupTimeout
+  var ready = false
+  while epochTime() < deadline:
+    var line: string
+    discard serverProc.outputStream.readLine(line)
+    if ReadySignal in line:
+      ready = true
+      break
+  if not ready:
+    serverProc.terminate()
+    serverProc.close()
+    serverProc = nil
+    raise newException(TimeoutError, "TR server did not start within " & $StartupTimeout & "s")
+
+proc getServerUrl*(): string =
+  if serverPort == 0:
+    raise newException(CatchableError, "Server not started — call ensureServer() first")
+  "ws://localhost:" & $serverPort
+
+when isMainModule:
+  echo "Starting TR server..."
+  ensureServer()
+  echo "Server ready at: ", getServerUrl()
+  echo "Sleeping 2s then exiting (addExitProc will kill server)..."
+  os.sleep(2000)
+  echo "Done."