docs(realtime): fix RealtimeRunner context docstring

[anxkhn]

RealtimeRunner.__init__ documented a context parameter in its Args: block,
but the constructor has no such parameter. Its real parameters are
starting_agent, model, and config. The context parameter actually belongs
to RealtimeRunner.run(), where it was moved in the [8/n] Make realtime more like the rest of agents sdk change, but its Args: entry was left behind on the
constructor and run() was never given one.

This misleads users of the realtime API into thinking they can pass context to
the RealtimeRunner(...) constructor.

This change:

• Removes the stale context: line from RealtimeRunner.__init__'s Args: block
  so it documents only the parameters the constructor actually accepts.
• Adds an Args: block to RealtimeRunner.run() documenting its real parameters,
  context and model_config, matching how the sibling RealtimeSession
  documents the same values.

Docs-only; no runtime, API, or behavior change.

Test plan

No executable behavior changes (docstring-only), so no new tests are warranted.
Verified the docstrings now match the real signatures by introspection, and ran
the standard checks on the changed file:

• RealtimeRunner.__init__ documented Args names now equal its real parameters:
  ['starting_agent', 'model', 'config'].
• RealtimeRunner.run documented Args names now equal its real parameters:
  ['context', 'model_config'].
• uv run ruff format --check src/agents/realtime/runner.py -> already formatted.
• uv run ruff check src/agents/realtime/runner.py -> All checks passed!
• uv run mypy src/agents/realtime/runner.py -> Success: no issues found.

Per AGENTS.md, docs-only changes may skip $code-change-verification.

Issue number

N/A (no existing tracker issue).

Checks

• I've added new tests, if relevant (N/A: docstring-only, no behavior change)
• I've run .agents/skills/code-change-verification/scripts/run.sh (N/A per
  AGENTS.md docs-only exemption; ran ruff format/check + mypy on the changed file)
• I've confirmed all verification steps pass
• If using Codex, I've run /review before submitting this PR (N/A)

---

The diff

diff --git a/src/agents/realtime/runner.py b/src/agents/realtime/runner.py
index e51a094..a6ec189 100644
--- a/src/agents/realtime/runner.py
+++ b/src/agents/realtime/runner.py
@@ -38,7 +38,6 @@ class RealtimeRunner:
 
         Args:
             starting_agent: The agent to start the session with.
-            context: The context to use for the session.
             model: The model to use. If not provided, will use a default OpenAI realtime model.
             config: Override parameters to use for the entire run.
         """
@@ -51,6 +50,10 @@ class RealtimeRunner:
     ) -> RealtimeSession:
         """Start and returns a realtime session.
 
+        Args:
+            context: The context to use for the session.
+            model_config: Override parameters to use for this session's model.
+
         Returns:
             RealtimeSession: A session object that allows bidirectional communication with the
             realtime model.