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/runner_process.nim

@@ -0,0 +1,61 @@
+## BattleRunner Java subprocess — capture stdout JSON-lines output.
+
+import std/[osproc, os, strutils, streams, times, net]
+
+const
+  DefaultRunnerJar = "/home/davide/Projects/tank-royale/runner/examples/lib/robocode-tankroyale-runner.jar"
+  ScriptDir = currentSourcePath().parentDir() / ".." / ".." / "tools" / "battle_runner"
+
+proc runBattleRunner*(serverUrl: string, botDirs: seq[string], rounds: int,
+                      timeout: int = 30000): string =
+  ## Starts TestBattleRunner as a subprocess. Returns captured stdout on success.
+  ## Raises IOError on non-zero exit or TimeoutError on timeout.
+  let jar = getEnv("TR_BATTLE_RUNNER", DefaultRunnerJar)
+  let classDir = getEnv("TR_BATTLE_RUNNER_DIR", ScriptDir)
+
+  let args = @[
+    "-cp", classDir & ":" & jar,
+    "TestBattleRunner",
+    "--server-url", serverUrl,
+    "--rounds", $rounds,
+    "--bot-dirs", botDirs.join(",")
+  ]
+
+  let p = startProcess("java", args = args,
+    options = {poUsePath, poStdErrToStdOut})
+  defer:
+    p.close()
+
+  let deadline = epochTime() + timeout.float / 1000.0
+  var stdout = ""
+  var line: string
+  while epochTime() < deadline:
+    if p.peekExitCode() != -1:
+      # Process finished; drain remaining output
+      while p.outputStream.readLine(line):
+        stdout.add(line & "\n")
+      break
+    if p.outputStream.readLine(line):
+      stdout.add(line & "\n")
+
+  if epochTime() >= deadline and p.peekExitCode() == -1:
+    p.terminate()
+    raise newException(TimeoutError,
+      "BattleRunner timed out after " & $timeout & "ms")
+
+  let code = p.waitForExit()
+  if code != 0:
+    raise newException(IOError,
+      "BattleRunner exited with code " & $code & "\nOutput:\n" & stdout)
+
+  result = stdout
+
+when isMainModule:
+  echo "runner_process.nim — usage:"
+  echo "  runBattleRunner(serverUrl, botDirs, rounds, timeout)"
+  echo ""
+  echo "Env vars:"
+  echo "  TR_BATTLE_RUNNER      JAR path (default: " & DefaultRunnerJar & ")"
+  echo "  TR_BATTLE_RUNNER_DIR  class dir (default: tools/battle_runner/)"
+  echo ""
+  echo "Cannot self-test without a running TR server. Start one first."