Exclude !post from the daily cap

Manual !post overrides were counted toward daily_cap_total, so a few
forced posts could starve the round-robin rotation for the rest of the
day. Tag forced rows in post_log and skip them in CountAllPostsInWindow
so the cap only meters the auto-rotation.

internal/storage/db.go

@@ -83,6 +83,7 @@ func runMigrations(d *sql.DB) error {
 	addColumnIfMissing(d, "stories", "paywalled", "INTEGER NOT NULL DEFAULT 0")
 	addColumnIfMissing(d, "stories", "published_at", "INTEGER")
 	addColumnIfMissing(d, "post_log", "url_canonical", "TEXT")
+	addColumnIfMissing(d, "post_log", "forced", "INTEGER NOT NULL DEFAULT 0")
 	addColumnIfMissing(d, "round_robin_state", "last_channel", "TEXT")
 
 	// FTS5 virtual tables don't support IF NOT EXISTS reliably.