feat: Build Early Access page with backend email capture

Combined page: countdown timer (Feb 28), email capture with server
count segmentation (wired to POST /api/early-access), Founding Admin
Program (25 slots), demo dashboard preview placeholders, roadmap
voting, and launch timeline. Backend: Axum handler, migration for
early_access_signups table with email + server_count + created_at.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/migrations/002_early_access_signups.sql

@@ -0,0 +1,9 @@
+-- Early access email capture with server count segmentation
+CREATE TABLE IF NOT EXISTS early_access_signups (
+    id UUID PRIMARY KEY DEFAULT uuid_generate_v4(),
+    email VARCHAR(255) NOT NULL UNIQUE,
+    server_count VARCHAR(10) NOT NULL,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX idx_early_access_email ON early_access_signups(email);