bug: unregistered tokens fire global fallback webhook

[peg]

Problem

When a request hits /c/{token} with a token that passes format validation but isn't registered in the database, the server still fires an alert to the global fallback webhook (cfg.WebhookURL).

Root cause

In processAlert:

webhookURL := s.cfg.WebhookURL // global fallback
if reg != nil && reg.WebhookURL != "" && reg.WebhookURL != "use-global" {
    webhookURL = reg.WebhookURL
}
if webhookURL != "" {
    deliverWebhook(webhookURL, e, reg)
}

When reg == nil (token not found), the fallback is used unconditionally. Any token-shaped URL path that passes the regex (^[a-zA-Z0-9_-]{8,80}$) will trigger a webhook delivery.

Observed behavior

• GET /c/agent-01- passes the regex (9 valid chars including trailing dash)
• Token has no registration in DB → reg == nil
• Global webhook fires anyway
• Alert appears in Discord with no agent identifier (just the bare prefix)

Fix

Only fire the webhook if the token is actually registered:

if reg == nil {
    log.Printf("CANARY_UNREGISTERED token=%s ip=%s — ignoring", token, ip)
    return
}
webhookURL := s.cfg.WebhookURL
if reg.WebhookURL != "" && reg.WebhookURL != "use-global" {
    webhookURL = reg.WebhookURL
}
if webhookURL != "" {
    deliverWebhook(webhookURL, e, reg)
}

Events can still be inserted for auditability, but unregistered tokens should never trigger webhook delivery.

Impact

• Alert fatigue / false positives from probe traffic
• Potential webhook spam from automated scanners probing URL patterns