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.

cli-config.yaml.example

@@ -507,6 +507,13 @@ agent:
   # finish, then interrupts anything still running after this 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. Lower this
+  # to 1 if you use fallback providers and want fast failover on flaky
+  # primaries (default 3). The OpenAI SDK does its own low-level retries
+  # underneath this wrapper — this is the Hermes-level loop.
+  # api_max_retries: 3
   
   # Enable verbose logging
   verbose: false