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/tips.py

@@ -289,6 +289,7 @@ TIPS = [
     "When a provider returns HTTP 402 (payment required), the auxiliary client auto-falls back to the next one.",
     "agent.tool_use_enforcement steers models that describe actions instead of calling tools — auto for GPT/Codex.",
     "agent.restart_drain_timeout (default 60s) lets running agents finish before a gateway restart takes effect.",
+    "agent.api_max_retries (default 3) controls how many times the agent retries a failed API call before surfacing the error — lower it for fast fallback.",
     "The gateway caches AIAgent instances per session — destroying this cache breaks Anthropic prompt caching.",
     "Any website can expose skills via /.well-known/skills/index.json — the skills hub discovers them automatically.",
     "The skills audit log at ~/.hermes/skills/.hub/audit.log tracks every install and removal operation.",