Make schema.sql self-migrating for forwarded_for column

[yellowman]

CREATE TABLE IF NOT EXISTS is a no-op on databases that already have a submissions table, so the forwarded_for column would never appear on an existing install. Add an idempotent ALTER TABLE ... ADD COLUMN IF NOT EXISTS so re-running schema.sql migrates older databases; it is a no-op on fresh installs.

Claude-Session: https://claude.ai/code/session_01EtMfJEmMXbwnUJ9p3uFXXN

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Note

Low Risk
Single additive, idempotent DDL line with no application logic changes.

Overview
schema.sql can now upgrade older databases that already had a submissions table but were created before forwarded_for existed.

Because CREATE TABLE IF NOT EXISTS does nothing on existing tables, those installs would never pick up the column from the table definition alone. This change adds an idempotent ALTER TABLE submissions ADD COLUMN IF NOT EXISTS forwarded_for TEXT plus a short comment that re-running the script is the intended migration path. Fresh installs are unchanged (the column is already in CREATE TABLE; the ALTER is a no-op).

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