hermes: HINDSIGHT_BANK_ID is ignored when config.json exists #5600

The README says HINDSIGHT_BANK_ID sets the bank. That only works when there is no config.json.

• With no config file, _load_config() builds the config from env vars and reads HINDSIGHT_BANK_ID.
• With a config.json (which setup writes), _apply_connection_settings uses bank_id, then banks.hermes.bankId, then "hermes". It never reads HINDSIGHT_BANK_ID, even when the file has no bank id.

So a user who sets HINDSIGHT_BANK_ID in their profile .env silently writes to and reads from the hermes bank. The same applies to the other env fallbacks in _load_config (HINDSIGHT_MODE, HINDSIGHT_API_KEY, HINDSIGHT_BUDGET...).

Decision needed: what wins, config.json or env? Suggested: an explicit value in config.json wins, and env fills any key the file leaves out. Then update the README to match.

Reported in the Hermes repo by @mkslzk (NousResearch/hermes-agent#51375, issue #51166) and @westkite1201 (NousResearch/hermes-agent#51173). Split out of #4662.