feat(security): make secret redaction off by default (#16794)

Flips security.redact_secrets from true to false in DEFAULT_CONFIG, and
the HERMES_REDACT_SECRETS env-var fallback in agent/redact.py now
requires explicit opt-in ("1"/"true"/"yes"/"on") to enable.

New installs and users without a security.redact_secrets key get pass-
through tool output. Existing users whose config.yaml explicitly sets
redact_secrets: true keep redaction on — the config-yaml -> env-var
bridges in hermes_cli/main.py and gateway/run.py still honor their
setting.

Also updates the inline config comments, website docs, and the
hermes-agent skill so /hermes config set security.redact_secrets true
is now the documented way to turn it on.

agent/redact.py

@@ -56,8 +56,12 @@ _SENSITIVE_BODY_KEYS = frozenset({
 })
 
 # Snapshot at import time so runtime env mutations (e.g. LLM-generated
-# `export HERMES_REDACT_SECRETS=false`) cannot disable redaction mid-session.
-_REDACT_ENABLED = os.getenv("HERMES_REDACT_SECRETS", "").lower() not in ("0", "false", "no", "off")
+# `export HERMES_REDACT_SECRETS=true`) cannot enable/disable redaction
+# mid-session.  OFF by default — user must opt in via
+# `security.redact_secrets: true` in config.yaml (bridged to this env var
+# in hermes_cli/main.py and gateway/run.py) or `HERMES_REDACT_SECRETS=true`
+# in ~/.hermes/.env.
+_REDACT_ENABLED = os.getenv("HERMES_REDACT_SECRETS", "").lower() in ("1", "true", "yes", "on")
 
 # Known API key prefixes -- match the prefix + contiguous token chars
 _PREFIX_PATTERNS = [
@@ -257,7 +261,7 @@ def redact_sensitive_text(text: str) -> str:
     """Apply all redaction patterns to a block of text.
 
     Safe to call on any string -- non-matching text passes through unchanged.
-    Disabled when security.redact_secrets is false in config.yaml.
+    Disabled by default — enable via security.redact_secrets: true in config.yaml.
     """
     if text is None:
         return None