fix(auth): downgrade expected transient states from warn to debug

[patrykkopycinski]

Problem

Two log.warn() calls in src/sse/services/auth.ts fire for normal, recoverable operational states:

Message	Condition
${provider} | N accounts found but none active	All connections are rate-limited; the caller receives allRateLimited: true with a retryAfter value and handles it.
No credentials for ${provider}	No active account was found; upstream combo routing or the circuit breaker handles this.

Both conditions are expected during normal operation with many provider connections and produce log noise at the warn level (visible by default), especially when rate limits are cycling.

Fix

Downgrade both calls to log.debug():

// before
log.warn("AUTH", `${provider} | ${allConnections.length} accounts found but none active`);
log.warn("AUTH", `No credentials for ${provider}`);

// after
log.debug("AUTH", `${provider} | ${allConnections.length} accounts found but none active`);
log.debug("AUTH", `No credentials for ${provider}`);

debug is the correct level: the surrounding code already handles both cases gracefully and the caller has full context. No information is lost — operators who need to diagnose auth flow can set APP_LOG_LEVEL=debug.