fix(async): replace get_event_loop() with get_running_loop() in async contexts

Follow-up to PR #21293 (cli.py), which fixed the same anti-pattern.
`asyncio.get_event_loop()` is documented as effectively "always returns
the running loop when called from a coroutine" and emits
DeprecationWarning/RuntimeWarning in some interpreter configurations.
The Python docs explicitly recommend get_running_loop() inside coroutines.

Replaces the remaining 9 call sites that are unconditionally inside
async def bodies:

- tools/browser_cdp_tool.py — _cdp_call() (4 sites): deadline + remaining
  computations inside the async websockets.connect context manager.
- hermes_cli/web_server.py — get_status, _start_device_code_flow,
  submit_oauth_code (3 sites): all FastAPI async endpoints offloading
  blocking httpx / PKCE work to run_in_executor.
- environments/agent_loop.py — HermesAgentLoop (1 site): tool dispatch
  inside the async rollout loop.
- environments/benchmarks/terminalbench_2/terminalbench2_env.py —
  rollout_and_score_eval (1 site): test verification thread offload.

All 9 sites are unconditionally inside async def bodies, so a running
loop is guaranteed and no try/except RuntimeError fallback is needed
(unlike the cli.py case in #21293, which ran from a background thread).

Behavior is identical on supported Python versions; aligns the codebase
with the post-#21293 idiom and avoids future warnings as the deprecation
hardens.

Salvaged from PR #21930 by @Zhekinmaksim onto current main (the
original branch was 109 commits behind and carried unintended
stale-branch reverts of unrelated landed changes — _tail_lines
encoding=utf-8 and the Windows PTY bridge guard). Only the 9 swaps
from the PR's intended scope are applied here.

environments/benchmarks/terminalbench_2/terminalbench2_env.py

@@ -575,7 +575,7 @@ class TerminalBench2EvalEnv(HermesAgentBaseEnv):
                 # other tasks, tqdm updates, and timeout timers).
                 ctx = ToolContext(task_id)
                 try:
-                    loop = asyncio.get_event_loop()
+                    loop = asyncio.get_running_loop()
                     reward = await loop.run_in_executor(
                         None,  # default thread pool
                         self._run_tests, eval_item, ctx, task_name,