Make Resend from-address config-only; drop credential status rows

The Settings page no longer renders the Resend From Address input or any
of the read-only "Set in config.toml" credential status rows (Apify key,
eBay id/secret, ntfy auth, Resend key). Those rows looked like editable
inputs but were dead text, and duplicated what the Test buttons verify
more authoritatively.

- resend_from is now sourced only from config.toml ([resend] from); it is
  removed from settingsKeys, the test-Resend handler, the scheduler email
  client, and the schema seed.
- Removed the credStatus templ component, the CredentialStatus field on
  SettingsData, and the credentialStatus() handler helper.

internal/db/schema.sql

@@ -116,8 +116,7 @@ INSERT OR IGNORE INTO settings (key, value) VALUES
     ('match_confidence_threshold', '0.6'),
     ('apify_cost_per_call', '0.00'),
     ('monthly_budget_usd', '0.00'),
-    ('resend_api_key', ''),
-    ('resend_from', '');
+    ('resend_api_key', '');
 
 -- apify_api_usage tracks Apify actor runs per UTC day so the operator (and
 -- every signed-in user) can see consumption and an estimated spend. Apify