feat(agent): make API retry count configurable via agent.api_max_retries (#14730)

Closes #11616.

The agent's API retry loop hardcoded max_retries = 3, so users with
fallback providers on flaky primaries burned through ~3 × provider
timeout (e.g. 3 × 180s = 9 minutes) before their fallback chain got a
chance to kick in.

Expose a new config key:

    agent:
      api_max_retries: 3  # default unchanged

Set it to 1 for fast failover when you have fallback providers, or
raise it if you prefer longer tolerance on a single provider. Values
< 1 are clamped to 1 (single attempt, no retry); non-integer values
fall back to the default.

This wraps the Hermes-level retry loop only — the OpenAI SDK's own
low-level retries (max_retries=2 default) still run beneath this for
transient network errors.

Changes:
- hermes_cli/config.py: add agent.api_max_retries default 3 with comment.
- run_agent.py: read self._api_max_retries in AIAgent.__init__; replace
  hardcoded max_retries = 3 in the retry loop with self._api_max_retries.
- cli-config.yaml.example: documented example entry.
- hermes_cli/tips.py: discoverable tip line.
- tests/run_agent/test_api_max_retries_config.py: 4 tests covering
  default, override, clamp-to-one, and invalid-value fallback.

hermes_cli/config.py

@@ -361,6 +361,15 @@ DEFAULT_CONFIG = {
         # to finish, then interrupts any remaining runs after the timeout.
         # 0 = no drain, interrupt immediately.
         "restart_drain_timeout": 60,
+        # Max app-level retry attempts for API errors (connection drops,
+        # provider timeouts, 5xx, etc.) before the agent surfaces the
+        # failure.  The OpenAI SDK already does its own low-level retries
+        # (max_retries=2 default) for transient network errors; this is
+        # the Hermes-level retry loop that wraps the whole call.  Lower
+        # this to 1 if you use fallback providers and want fast failover
+        # on flaky primaries; raise it if you prefer to tolerate longer
+        # provider hiccups on a single provider.
+        "api_max_retries": 3,
         "service_tier": "",
         # Tool-use enforcement: injects system prompt guidance that tells the
         # model to actually call tools instead of describing intended actions.