fix(sso): 🐛 confirm missing emails by link, fix button contrast and logos

- Replace the six-digit code with an emailed confirmation link, matching
  VitNode's existing email verification. The link works for 30 minutes,
  once, and only in the browser that started the sign-in (prevents
  account pre-hijacking); a link opened elsewhere explains why.
- Rework the pending table (confirmHash/confirmExpiresAt/...) and
  regenerate the unreleased migration.
- Reddit and GitLab become neutral buttons with their colored mark, Kick
  uses its black and green, Slack gets its four-color logo, so no button
  label ends up dark-on-color.
- Center the "Check your email" state, add a mail icon to the email input
  and icons to "Send a new link" and "Use a different email".
- Update docs and screenshots for the link flow.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S9WHKDMZd6SGLUjdYbi4hT

Author: claude

…1_sso_attempts_and_pending/migration.sql …7_sso_attempts_and_pending/migration.sqlapps/api/migrations/20261023190631_sso_attempts_and_pending/migration.sql renamed to apps/api/migrations/20261030153537_sso_attempts_and_pending/migration.sql apps/api/migrations/20261023190631_sso_attempts_and_pending/migration.sql renamed to apps/api/migrations/20261030153537_sso_attempts_and_pending/migration.sql

@@ -18,11 +18,10 @@ CREATE TABLE "core_sso_pending" (
 	"providerUsername" varchar(255),
 	"profile" jsonb,
 	"email" varchar(255),
-	"codeHash" varchar(64),
-	"codeExpiresAt" timestamp,
-	"codeAttempts" integer DEFAULT 0 NOT NULL,
-	"codeSends" integer DEFAULT 0 NOT NULL,
-	"codeSentAt" timestamp,
+	"confirmHash" varchar(64),
+	"confirmExpiresAt" timestamp,
+	"confirmSends" integer DEFAULT 0 NOT NULL,
+	"confirmSentAt" timestamp,
 	"createdAt" timestamp DEFAULT now() NOT NULL,
 	"expiresAt" timestamp NOT NULL
 );